Transcript for:
Physics Regents Exam Review

thank you okay good afternoon [Music] this live stream I'm going to be going over the June 2022 physics regions so hopefully those you guys that watch this find this interesting um when this gets saved to YouTube you can just like skip ahead I guess to the parts that you want to review so I'm going to be going over every question and also kind of explain some of the stuff going on so the physics behind each question so the physics regions this year for 2020 3 is this Thursday on the 22nd um and what I tell my students is there's like 50 multiple choice questions and the rest is short answer so I'm not sure what the curve is going to be like this year but these are the things that you're going to be given on the regions a scientific or graphing calculator uh ruler or straight edge protractor and then the 2006 edition of the reference table so let's start the first question first question says what is um basically what a scalar quantity is it says which terms Identify two scalar quantities so first thing that I need to know about this question is that scalar quantities are values with magnitude only and magnitude this word magnitude means size or amount so this is not allowed to have any direction scalar quantities can be negative or positive they just can't have directions associated with them if there's a direction associated with um a measurement is called a vector so vectors have magnitude and direction within their values so let's look at these choices here we have Choice One says force and acceleration Choice two says impulse and distance choice three says mass and velocity and choice four says energy and time so two scalar quantities meaning both of these quantities need to be scalar so magnitude only I know that Force has Direction and so does acceleration acceleration can be East forces can be south or forward or backwards velocity is also the same thing so that eliminates choice three and choice two um choice three and choice one so for Choice two and choice four I know a distance is a scalar quantity I don't know time is a scalar quantity the answer Choice here is four Choice four energy and time are both scalar quantities impulse has Direction so that makes it a vector it can have Direction all right less number one so for number two number two says a motorcyclist initially traveling East at 15 meters per second accelerates uniformly at a rate of three meters per second squared East to a velocity of 21 meters per second East how far does the motorcyclist travel while accelerating and then I see my answer choices are in meters what's a good tip to look at what your answer choices are in so it kind of indicates what you're solving for I see meters so I know that it's distance also this how far means distance so distance is my unknown so I'm going to write that down that's what I'm solving for there's a whole bunch of other variables that are given here it says initially traveling East at 15 meters per second initially traveling East at 15 meters per second means that the initial velocity is 15 meters per second I'm going to put East here and I'll explain why in a second then it says the motorcyclist accelerates uniformly at a rate of three meters per second squared East so that is my acceleration acceleration is three meters per second squared East as well and then it says to a velocity of 21 meters per second East so everything is East here this actually makes it pretty simple so this is my final velocity which is 21 meters per second East now when there's Direction involved and the question doesn't say like What's the magnitude or whatever you have to take into consideration the direction especially with the formula that we're going to be using so since East is kind of this way and West is this way we're going to say that East is our positive direction and therefore West since its opposite will be our negative Direction so we can convert all these values 15 meters per second East to just positive 15 meters per second drop that East three meters per second squared East we drop the East and we can say positive three meters per second squared and 21 meters per second East would be positive 21 meters per second so we can get rid of these East and just add a positive obviously if the question had other directions you'd indicate if they're positive or negative for the calculation now for this problem off the top of my head I might not know what formula I want to use so I'm going to bring up my reference table here's the reference table and I'm going to scroll down to page six that's the last page page six here has the mechanics and energy and momentum formulas that are present so I'm looking on my reference table for these variables I'm looking for d v i a and v f so that happens to be this um formula here let me just highlight it this one so I'm going to write that down I'm going to write down VF squared equals v i squared plus two a d and since I'm solving for distance what I'm going to do is I'm just going to rearrange the formula so I tell my students that it's better to rearrange the formula first before substituting values to eliminate any math errors so I need to solve for D here so I have this whole term I want to move to the other side so v i squared I'm going to subtract on this side and I'm going to subtract v i squared on this side this cancels out on the left side I'm left with v f squared minus v i squared equals and then 2ad comes down so 2ad and then in order to get d by itself I can just divide by 2 a that cancels the 2A at the top and the bottom and I'm going to do the same thing to the left side of the equation so this whole left side gets divided by 2A I'm going to be left with d equals VF squared minus v i squared divided by 2 a okay so that's my formula I'm going to substitute I'm going to substitute all these values in here now because this is a multiple choice question this question has a lot of work that we're doing for it uh you don't need to show any work for that on the regions you use it just bubble in your answer sheet but I'm going to show all the substitution here so VF squared is going to be 21 meters per second this whole number is squared minus v i that's 15 meters per second that whole number is squared and then I'm dividing the whole thing by 2 times 3 meters per second squared so three meters per second and only a seconds here is squared okay so now I need to put this in my my calculator because I can't do that type of math in my head so I'm going to do the numerator first so 21 squared minus 15 squared that gives me 216 216 is my numerator there's some units here the units is that and then the denominator is just 2 times 3 which is six okay so I'm going to do 216 divided by 6. and that gives me 36 meters so let's see if we have that as an answer and that is choice three okay so with these types of problems where you have to use the reference table and substitute numbers or values or quantities as variables be careful when you're doing your math or your algebra okay so let's move on the question three question three says a battery powered electric motor is used to cause the wheels of a toy car to rotate in this motor there is a conversion of Choice One says mechanical energy to electrical energy Choice two says electrical energy to chemical energy choice three is thermal energy to electric energy interest fours electric energy to mechanical energy so for this type of problem this type of energy conversion stuff I always like to um think of it as a before and after situation so there's a before situation and then it something happens then there's an after situation the energy conversion so in the before situation the problem says that there's a battery powered electric motor it can't be any more clear than that this has to do something with electric energy okay and then the after situation is it says it causes the wheels of the top toy car to rotate so Wheels rotating that has to do with some type of motion so there's electric energy converting to motion so immediately we can eliminate choices one and three because electric energy is not first we said that because that there's an electric a battery powered electric motor that electric energies are first thing so that leaves Choice two and choice four motion is related to some mechanical energy process so in this case the answer is Choice four electric energy to mechanical energy so that's the answer all right for number four it says a projectile is launched horizontally from a height of 65 meters with an initial horizontal speed of 35 meters per second what is the projectile's horizontal speed after it has fallen 25 meters neglect friction so this type of problem that I'm just going to draw a really quick setup here we have some type of 65 meter um height here's our projectile it's being launched horizontally initially and it's going to fall something like that so with this initial horizontal and I'll call vix initial VI and X for the horizontal or X Direction something to note when it deals with projectile motion then the horizontal Direction okay in the horizontal Direction velocity is constant and that is because there is no horizontal acceleration and the reason for there's no horizontal acceleration is because there are no horizontal forces in the X Direction propelling the object horizontally so that is all to say that velocity Remains the Same so if our initial velocity is is 35 meters per second that is going to be the speed at every point along this uh trajectory in the horizontal Direction so it's going to be 35 meters per second there 35 meters per second there and when it hits the ground it'll hit the ground at 35 meters per second so the answer here is Choice 2 35 meters per second let me rewrite that all right for question five question five says the diagram below represents two forces F1 and F2 acting concurrently on a block sliding on a horizontal frictionless surface and then there's a diagram it says which statement describes the motion of the block Choice One says the block is accelerating to the right choice 2 says the block is accelerating to the left charge 3 says the block is moving to the right with constant speed and choice 4 says the block is moving to the left with decreasing speed so all these different answers so here's how we approach this type of problem so just as a hint this is a Newton's Second Law problem so we can apply a Newton's Second Law here we have this diagram here where there's opposing forces and they're equal and by the way concurrent means at the same time let me write that down concurrent means at the same time we also have this Vector here indicating that the speed of the block is to the right the velocity of the block is to the right actually so if we apply Newton's Second Law because we see that there's some acceleration um choices here acceleration according to Newton's second law is the net force divided by Mass and in this case the net force is the sum of all forces acting on an object and to some means you just add up Okay so if we add up these forces we're going to have f 1 plus f 2. I replace F net with F1 plus F2 furthermore because um F1 is pointing to the right and F2 is pointing to the left one of them has to be negative since it's opposite so let's pick F2 to be negative so when we substitute these values in here we're going to get F1 equals 10 Newtons and F2 equals negative 10 Newtons since it's opposing F1 so in this case we just get 0 in the numerator and zero divided by m we don't need to care about the mass is zero so the acceleration is zero meters per second squared so that eliminates Choice one and two because it says that the block is accelerating so it's not Choice One or Choice two choice three and choice four are also different um even though they talk about speed one is talking about constant speed that's choice three and choice four is talking about decreasing speed when we have a no acceleration zero acceleration means the speed does not change actually this means the velocity doesn't change the velocity does not change so decreasing speed that cannot be possible so the answer here is choice three for number six number six says the magnitude of an unbalanced force applied to a four kilogram crate is 10 Newtons if the magnitude of this applied unbalanced force is doubled what is the inertia of the crate okay inertia is a measurement actually I got that backwards Mass is a measurement of an object's inertia okay so they're basically the same thing in taking the physics regions you can understand that inertia equals mass so we can say that inertia equals mass so if we have a mass that is four kilograms and it's asking for what's the inertia and nothing's happening to the mass then nothing is going to happen to the inertia so the inertia is also unchanged the mass doesn't change so therefore the inertia doesn't change for number seven number seven says a 60 kilogram Mass man is pushing a 30 kilogram lawnmower compared to the magnitude of the force exerted on the lawnmower by the man the magnitude of the force exerted by the man on the man by the lawnmower is blank and then we have some fraction answers one quarter is great one-half is great the same or twice is great this is a spoiler alert this is Newton's third law and Newton's third law says for every action there's an equal and opposite reaction what that means is that if there is a force applied from one object let's call it a and it's applied on object B that is going to be equal to the force of object B on object a and then we add this negative sign to show that it's in opposite direction in class it looks like there's a table there's a box on the table it's at rest the box is pushing down on the table and the table is pushing back on the box and then the Box doesn't move because it's in equilibrium so in this example here we have the force of the box on the table and that is equal to the opposite force of the table on the box so they're just opposite in directions but they're equal in magnitude so in this case the answer is the same since the question is asking for the magnitude of the force exerted on the man by the lawnmower is going to be equal to the same number as the lawnmower on the man all right um that's number seven so for number eight number eight I already see a circle here so I should start thinking about centripetal motion it says the diagram below represents a roller coaster car traveling counterclockwise and a vertical circle when the car is in in the position shown what are the directions of the centripetal force acting on the car and the velocity of the car and then the choices go on to say the directions for the centripetal force and the directions for the velocity so two things to know about centripetal motion is the centripetal force and whoops not f a FC so the centripetal force and the centripetal acceleration point towards the center of a circle so the centripetal force and the centripetal acceleration both Point towards the center of the circle the reason for that is because they're dependent on one another the other thing is that any velocity of an object points tangent to the circle so if we have a circle here okay that's my circle there's the center of my circle let's say we have an object at this point here it's moving around this circle let's say it's moving around this way clockwise okay whoops that's not what I want whatever that's fine it's going around that way so at this point the force points to the center of the circle and since it's moving around the circle like that clockwise the velocity is going to point tangent in this direction so that's velocity okay in this diagram here we have a counterclockwise um motion and to the center of the circle would be here so this is where the Force points and tangent to this circle would be down this way so that is my velocity okay so we're going to look for a choice that says force is pointing to the right since the center of the circle relative to that position is to the right so that happens to be Choice One all right for number nine number nine says an electric motor with a power rating of that many watts is used to raise an elevator weighing that many newtons at constant speed what is the total time required for the motor to raise the elevator a vertical distance of 20 meters and then I have four choices and all of the choices are in seconds so let's write this down let's write down my Givens here so I have an electric motor with a power rating of that so that's power equals 6.48 times 10 to the four Watts what's that is used to raise an elevator weighing that's the weight this many newtons so this is my weight I'm going to put f with a little G some people might use W as well but because I still I have this as Watts I don't want to put weight as W so I'm going to use f g as my weight so this is going to be 2 point 8 times 10 to the 4. Newtons what is the total time required for the motor to raise the elevator a vertical distance of 20 meters so this is distance or height height is also vertical distance 20 meters and time is my unknown okay so for this I need to go to the reference table because I don't memorize some of these formulas so let's go to the reference table reference table on this page still on page six is the mechanics section even though it mentioned something about electric motor we're talking about weight and distance so that's mechanics so I'm looking for capital P power um in case I forgot what these symbols mean the indications are on the right the definitions are there on the right so power there's only one equation on page six that includes power and it's this one and I'm looking for what variables I have I have power force distance and time so here's power here's Force distance and time so let me write that formula down so power equals force times distance over time now because I need to solve for time I'm not solving for power I'm solving for time I want to rearrange this formula so I'm going to cross multiply so to solve for T cross multiplying is the numerator on the left times the denominator on the right and then the numerator on the right times the denominator on the left since this is just one variable on the left I can put an imaginary um over one there so I'm going to be left with P times T equals F times D and then to solve for T I need to divide by P so they cancel out and I'm left with the formula of T equals f d over p so force times distance divided by power so this is what that looks like force is 2.80 times 10 to the 4 Newtons distance is 20 meters and power is 6.48 times 10 to the 4 Watts all right so here's a tip this is a math Tip since I'm just multiplying and dividing everything here there's no addition or subtraction I can see that there's 10 to the 4 on the numerator here and there's 10 to the 4 in the denominator so since it's 10 to the 4 divided by 10 to the 4 they actually cancel out so this will make my calculation that I'm going to put in my um calculator just 2.8 times 20 divided by 6.48 so this avoids that mistake of using um scientific notation so let's put that in 2.8 times 20. and then I'm dividing by 6.48 and I got an answer of 8.64 the rest of the numbers don't matter so 8.64 and since this is time that's seconds so I'm going to look for Here Choice 3 has that exact answer 8.63 seconds all right for number 10 number 10 says a person standing on a sidewalk here's the siren of an ambulance as it approaches passes by and goes away from the person compared to the excuse me compared to the frequency of the sound emitted by the siren the frequency of the sound observed by the person during this event is higher only lower only first higher then lower or finally first lower than higher so for this question um tasnine this is like a software it's called Ti Smart View [Music] um you could get it from the like the ti website uh but I don't think it's free anymore it was free during covid but I don't think it's free anymore but you can use something like Desmos if you want to um use like a graphing calculator so for this this question here has to do with a phenomenon called a Doppler effect so for 10 this is the Doppler effect Doppler effect the Doppler effect is defined as an apparent shift and a whoops an apparent instead of shift we'll say an apparent change in frequency of a wave when it's source is in motion so ordinarily when an object is at rest so let's say does that rest here's an object and it's let's say it's a speaker and it's making sound waves the frequency is going to be constant okay however when an object starts moving so let's say that the object is moving this way when an object starts moving the frequency changes um uh according to an observer so it's not a real change in frequency it's just an apparent change in frequency because of the nature of waves so let's say it's moving to the right the frequency over here will be higher and the frequency over here will be lower so on this side we have a higher frequency and on this side we have a low frequency so if there is an observer here and this object is approaching it and then it's going to pass it first it's going to hear a high frequency and then it's going to hear a low frequency if this whole object is moving towards it and then away from it so in this case we're going to have choice three as our answer for number 11 number 11 says which particles exhibit properties of waves in some experiments Choice One says photons only choice two says electrons only choice three says both photons and electrons and choice four says neither Photon Photon photons nor electrons for number 11 this category or this topic in physics is called wave particle duality and what this says is some particles act like waves so for example particles can collide right and transfer energy from one to another and waves have like eight different phenomena that they can exhibit one of them is like interfering so this is something to just kind of know and it's based on this um experiment called the double slit experiment when you guys are doing your studies you can look this up this is what um discovered that particles act like waves um and that's both photons and electrons so those are some of the particles that will act like waves all right for number 12 number 12 says the direction of the electric field at a point in space is defined as the direction of the force exerted by the field on a one test Mass located at that point Choice two says Magnetic North Pole located at that point Church 3 says negative test charge located at that point and choice 4 says positive test charge located at that point so when it comes to this this is also based on just something you have to know this is based on some experiment in the past where they had some charged object and it was unknown they didn't know what the charge of Q was they wanted to know if it was positive or negative or something and so what happened was they decided to choose uh positive particle and place it near this object and see what would happen to the positive particle so this object pushed it away and then they moved the positive test particle over here and they see that this charge object pushed it away and then they moved it over here and they see that it pushed it away and everywhere they moved it it kept pushing it away so they concluded that this object here must be positively charged and they were able to map electric fields how electric fields for positive objects go outwards and for negative objects the electric field lines go inwards so the answer here is Choice four Choice one doesn't make any sense because electric fields and electric forces don't depend really on the mass they depend on the charge of the object and then the other choices are just wrong choice two and choice three so answer here is choice for positive test charge located at a point all right for number 13 number 13 says a net force of one newton will accelerate a one kilogram mass at one meter per second squared accelerate one kilogram mass at 9.8 meters per second squared lift a one kilogram Mass vertically at a constant speed of one meter per second or lift a one kilogram Mass vertically at a constant speed of 9.8 meters per second so for this if we're talking about a net force and it's equal one newton we can use um Newton's second law slightly arranged F net equals mass times acceleration and so if this side equals one newton we need to figure out what times what will also equal one well if we look at these answer choices here we'll see this first one if we plug in one kilogram for the mass and one meter per second squared for the acceleration one times one equals one so that is Choice one the other ones um don't really allow a net force of one newton for number 14 number 14 says the elongation of a spring will be quadrupled if the magnitude of the force elongating the spring is quartered half doubled or quadrupled for number 14 we need to know that quadrupled means four times as much so it's four times greater and also elongation elongation means stretch so this is a spring that's being stretched so Let me refresh my memory on what the formula is for Springs stretching that is this formula right here force on a spring equals K times x so let's write that down force on a spring equals K which is the spring constant and times x so I need this formula because this is actually a proportion problem um so what I'm gonna do is I'm going to rewrite k I'm going to rewrite FS and I'll write X X in parentheses like this and the reason why is because the problem says that the elongation of the spring will be quadrupled that means that X is being times or multiplied by four so now there's a four coefficient of 4 on the right side of my equation in math if we do something to one side of an equation we must do the same thing to the left side of or the other side of the equation so in this case if we multiply the right side by 4 we have to multiply the left side by four since f is the only variable on the left side we can conclude that the force elongating the spring is also quadrupled for number 15 number 15 says the vector diagram below represents the path and distances run by a student in a cross-country race and then we have a diagram this student starts here they go some kilometers this way then South and then East and then South and then West to a Finish Line question says the displacement of the student from start to finish is and then if I look at my answer choices I see that everything has some unit of kilometers as well as a direction north south north south so usually kilometers is a unit that you would want to convert to meters however since the answer choices are in kilometers we don't need to do any type of conversions so we're going to write down number 15. and I'm gonna crudely uh recreate that drawing so we have a start here it goes this way then it goes this way then it goes this way this way and then all the way back here okay and there's my Finish Line so this is 0.80 this is 0.80 this is one kilometer this is 0.60 and this is 1.80 kilometers and then we have this nice little compass over here to indicate our Direction so if this is our starting point up here and we end up down here our displacement since that's what the question is asking for is going to be a straight line path from start to finish that's what displacement is defined as displacement is a straight line path from point A to point B so we'll just say from A to B in this case our starting point is point a and our finish point is point B so all we need to do is figure out what this length of this line is and we can use the rest of the diagram to figure that out so we can see that this section here corresponds to this number so this is 0.80 kilometers and this section here corresponds to this number which is 0.60 kilometers so we're using a little bit of geometry to figure this out so our displacement is going to be 0.80 kilometers plus 0.60 kilometers this equals uh 1.4 0 kilometers now since we started up at one point up here and then we did all these like east west south um movements we ended up our final position relative to our starting position is actually South of our starting position so our final position relative to our initial position is South so in this case we choose Choice two as our answer let's move on to number 16. number 16 says the diagram below shows the arrangement of three charged hollow metal spheres a b and c the arrows indicate the direction of the electric forces acting between the Spheres what spheres have static charges of the same sign so since we're talking about charges um the two things we need to know about charges or electrostatic forces Electro static uh forces is that like charges will repel so that's like two negative charges or an electron an electron or a negative four coulomb and a negative one coulomb they will repel um opposite charges will attract and so that's an example of let's say it was negative four coulomb and positive one coulomb those charges will attract or a electron and a positron okay so we are looking for what we mean by repel repel means that the arrows are pointing in opposite direction and what we mean by attract is that the arrows are pointing in uh like towards each other so we're going to look for that to be the case A and B have an attraction so they are oppositely charged B and C have an attraction so they're oppositely charged A and C are the only ones that repel so therefore these must be the same sign so we're going to say A and C only which is Choice two all right number 17 says two small charred spheres are located distance D from each other and experience an electrostatic force of attraction f e if the magnitude of charge of each sphere is tripled and the electrostatic force is unchanged what other change must have occurred so for number 17 this is another proportion problem and I'm gonna go to my reference table so that way I can find this formula that we need which is going to be on page four for our electricity so this is Page four under electricity we're going to see uh hold on okay yeah under electricity we're gonna see that Force equals k q1 Q2 over r squared and what we're going to use for this is we're going to do something similar to what we did with what question was that question 14 we're going to see when we change one variable or a few variables what happens to the other variables in this case the question is saying that um Fe is unchanged so that means since there's a invisible one in front of this Force whatever we do to the right side there the numerator the denominator need to be equal so that way they cancel out and equal one on that side so that way the force is unchanged so we see that um what does it say so it says the magnitude of the charge of each sphere is tripled so that means that we have the magnitude of charge one and the magnitude of charge 2 both tripled and the denominator I'm going to be r squared technically it's D um should be D Squared since that's the variable used in the problem but I'll just keep it as R so just to simplify this this is going to be nine three times three is nine times K times q1 times Q2 over r squared okay so there's a 9 on the numerator here and remember we need to do something to maintain that the left side doesn't change we don't actually want to multiply by um nine on the left side so the only other way to get rid of this 9 is to have a 9 on the denominator like this because 9 divided by 9 will equal one but in order for that to happen there needs to be our distance three times as well because this Square gets distributed so 3r squared equals so this gets distributed and this gets distributed so this is 9 r squared so this would um make it so our left and right side uh are kind of balanced out so in this case what we would do is that the distance was increased by a factor of three distance was increased by a factor of three since that's what we did here okay that's number 17. for number 18. number 18 says compared to the resistance of an aluminum wire at 20 degrees Celsius the resistance of a Tungsten wire of whoops I forgot to get rid of the reference table um so that's choice three for number 17 sorry for number 18 it says compared to the resistance of an aluminum wire at 20 degrees Celsius the resistance of a Tungsten wire at of the same length and diameter at 20 degrees Celsius is approximately the same twice as great one-half is greater or four times it's great so we're talking about aluminum wire and a Tungsten wire so and then this 20 degrees Celsius thing actually has to do with the reference table so let's bring this back up aluminum and tungsten are on this page for the same page as electricity the resistivities at 20 degrees Celsius and we see aluminum here and we see tungsten here so I'm going to write those values down so we have the resistivity of aluminum equals 2.82 times 10 to the negative 8 units are that and the resistivity of tungsten is 5.60 times 10 to the negative eight units are that okay so the other formula that we might maybe need is this formula that resistance equals resistivity times length divided by cross-sectional area now since the length of the area are the same and the only thing changing is this variable right here that's the only thing that's changing it's um 2.82 and then the rest of that and then 5.6 and then the rest of that it says compared to the resistance of aluminum the resistance of tungsten is approximately what so something I can see here is that these values um aren't that different except for the coefficients right so 10 to the negative 8 and 10 to the negative 8 and then ohm meters and ohm meters so what I can do here is just compare compare these two values I can use the calculator actually to come up with that comparison so if I take 5 .6 and I divided it by 2.82 those are the coefficients I'm dividing by I get some number which is 1.98 so this is if I were to take the resistivity of tungsten and divide it by the resistivity of aluminum I get this number which is approximately two so that's the comparison right tungsten to aluminum since that's what it's asking for asking for a comparison of tungsten to aluminum so the answer is going to be twice as great since that's close to 2. all right for number 19 number 19 says how much energy is expended when a current of 5 amperes is in a 5 Ohm resistor for five seconds so let's write down these variables how much energy is expended so energy when dealing with mechanics is e but when dealing with electricity and um electrostatics it's usually w okay for the work so this might be what we're solving for let me put that down maybe it's what we're solving for um it says when a current of 5 amperes so 5 amperes is in a 5 Ohm resistor so 5 ohms four five seconds that's my time so five seconds so everything is five here I'm gonna oh I forgot to take off the calculator um so this is question 19. so for this equation from the reference table I'm using I'm looking for work I'm looking for current I'm looking for resistance and I'm looking for time and that happens to be this formula right here work current resistance and time so let me write that down so work equals current squared times resistance times time so I'm solving for this so I can just multiply everything so this is going to be five amperes squared times five ohms times five seconds so five times five times five times five this is five to the fourth power which is 625 joules well let's write that down 625 all right for number 20 number 20 says the amount of electric current through an unknown resistor may be measured by connecting so when we want to measure current ammeters measure current and voltmeters measure measure potential difference or voltage potential difference voltage okay now the ammeter must be connected in series meaning it must be along the same Branch as the thing it wants to measure and volt meters must be connected parallel or in parallel to the thing it wants to measure that means you need to create a new Branch so the only thing that follows the only choice that follows both of those rules is an ammeter in series with the resistor so Choice one is number 20. all right let's move on to number 21. number 21 which phenomenon represents a wave spreading out behind a barrier as the wave passes by the edge of the barrier so what this represents is diffraction okay and the other ones the other ones don't really fall into that definition so you can answer this with the process of elimination reflection is when the wave reverses Direction um interference is when two waves add or subtract and refraction is when the wave changes speeds so diffraction is the only one by process of elimination that bends and the whole thing is you have a barrier here with some type of opening this is the edge of the barrier that they're talking about and you have these waves coming in and these waves will hit this and then as they get through this barrier they will bend around the barrier kind of I like to think about it like squeezing through all right for number 22 22 is a one kilometer length of copper wire a with a cross-sectional area of that meter squared it has a resistance of 0.172 ohm at 20 degrees Celsius another copper wire B is half as long and twice the cross-sectional area of wire a what is the resistance of copper wire B at 20 degrees Okay so that formula that we just borrowed we used here this one it seems like we might need to use it here so I'm going to rewrite that that is resistance equals resistivity times length divided by area now so this is wire a not to be confused with the area so wire a and wire B okay so they're both copper okay um wire a is one kilometer in length so length equals one kilometer this is one thousand meters all right that's something we need to convert and it says it has a cross-sectional area so area of one times ten to the negative 4 square meters and it has a resistance of 0.172 ohms okay now it says that wire B is half as long so this is L divided by two let's put that there and it says that the area is twice so area is two times the area what is the resistance of B okay so if we look at this formula and since this number here okay is [Music] 0.172 ohms we're going to use a as a basis the first one and what we're doing is resistance is the same so that doesn't matter but the length is half so I'm going to put l over 2 instead of 500 so L over 2. is 500. and my area is 2 times the area if I simplify this right this denominator here and this denominator here this will combine so on the numerator we'll have rho times whoops the length over and on the denominator we're going to have 4 I forgot to change the color I'm gonna have four times the area okay so this forces on the denominator because this is what happens when you combine the two times two we'll have four in the denominator here so if we have 0.172 Ohms on the left side and we have a 4 on the denominator on the right side we need to divide this side also by four and this will give us our answer what the resistance is so the resistance is going to be 0.172 divided by 4. so the resistance of B is going to be the resistance of a divided by 4 which in this case is 0.172 ohms over four and let's see what that is in the calculator so 0.172 divided by four and we get 0.043 so let me write that down 0.043 ohms and that answer is this choice right there so it seems like this Region's had a lot of proportions on it um there's a lot of math involved here and not too many like crazy physics so for number 23 number 23 says the magnitude of electric force exerted on a small positive charge located between two oppositely charged parallel plates is one smallest near the positive plate two smallest in the negative plate three greatest midway between the plates four the same everywhere between the plate the answer here is everywhere between the plates so when you have two parallel plates and let's say this one is positively charged this one's negatively charged and we have like the electric field lines that go like this this is just a property of parallel plates they have a uniform this means constant electric field and electrostatic force in between the plates so everywhere in between the plates is going to have the same electric field and the electric force for number 24 number 24 says an acoustic an acoustic organ as a musical instrument with pipes the oscillation of air molecules and the pipes of the organ produces sound waves that are electromagnetic longitudinal electromagnetic transverse mechanical longitude and mechanical transfers so sound waves are not electromagnetic and furthermore sound waves are longitudinal waves so for number 24 the thing to remember is sound waves are mechanical and compression or longitudinal waves okay 25 says which list identifies portions of the electromagnetic spectrum in order of increasing frequency so increasing frequency I need the reference table for this so let's bring up the reference symbol electromagnetic spectrum up here has so increasing frequency means we start with radio waves then go microwaves um so radio waves then microwaves then infrared then visible light then ultraviolet then x-rays then gamma rays so if I look at these choices here increasing frequency I see that gamma rays are included first gamma rays are like the highest frequency wave so one and four are eliminated and then I see two and three have gamma rays at the end so for choice three choice three has infrared visible ultraviolet gamma ray if I look at the reference table it goes infrared visible ultraviolet gamma rays so that is the answer foreign number 26 number 26 says a tuning fork is used to produce a sound wave having a frequency of 517 Hertz what is the wavelength of the sound wave in air at STP okay so for this it wants me to figure out the wavelength it also gives me the frequency which is 512 Hertz and for sound if I need the speed of sound that is on the reference table on page one so page one has the speed of sound in STP or at standard temperature pressure that's this right here we see that it is 3.31 times 2 times 10 to the 2 meters per second let's write that down that is 3.31 times 10 to the 2 meters per second I also need to go to another page on the reference table since I don't remember this formula so I'm going to go to page five of the reference table to look for a formula that has speed frequency and wavelength that happens to be this first Formula here on waves this is the wave speed formula so that is V equals frequency times wavelength I'm going to rearrange this formula to solve for wavelength that rearrangement looks like this okay so I'm going to divide by frequency on both sides and that gives me and that cancels out that gives me wavelength equals velocity divided by frequency the speed is 3.31 times 10 to the 2 meters per second and the frequency is 512 Hertz 10 to the 2. so let's bring out my calculator we have three point three one times ten to the 2. I'm going to use this shorthand notation I'll show what it looks like when you use that scientific notation and whatnot and divide by 512 we get that answer uh is that right let me just double check yeah that's right okay and then if I wanted to show the scientific notation like the regular times 10 to that that looks like 3.31 times 10 to the two then what I'm going to do is I'm going to make sure that there's parentheses around this okay because I don't want to mess up my calculation when you use this the times 10 to the exponent make sure you put that term that value in parentheses now I'm going to divide this by 512. and then I get the same answer sometimes when you don't use parentheses you will not get the correct answer so be careful with that so that answer 0.646 meters is Choice One okay moving on to question 27 27 says an amplified sound wave produced by an opera singer shatters a glass which phenomenon best represents this event with some of the other questions that we answered we can eliminate diffraction and we can eliminate reflection so in this case the answer is resonance resonance is really associated with wine glasses and opera singing and matching frequencies so in this case resonance is um vibrating objects or particles particles at a certain frequency frequency that causes nearby particles to also vibrate and then what happens is all these vibrations add up so you get a huge amplitude a lot of energy happening and then that's when the wine glass shatters so that's resonance all right for 28 28 says the diagram below represents a wave traveling in a rope in the direction indicated which arrow represents the motion of a particle at Point P at the instant shown so this is a transverse wave and transverse waves have perpendicular motion transverse waves so we have perpendicular perpendicular motion relative to the motion of the wave so the motion of the particles are perpendicular to the motion of the wave um so if the wave is moving to the right as indicated in this problem the particles will oscillate up and down so that eliminates Choice One and choice three in this case here if we have a wave and this is the way that I like to do it if we have a wave and it's moving to the right I'll kind of like redraw this wave shift it over to the right like this and I'm going to draw now an arrow from this point to where the new wave is so that's up there so that's the answer Choice four for number 29 number 29 says if several resistors are connected in series in an electrical circuit the potential difference across each resistor varies directly with the resistance of each resistor varies inversely with the resistance of each resistor varies inversely with the square of the resistance of each resistor or is independent of the resistance of each resistor oh boy okay so it says it's connected in series so the series rule for potential resistance is this um a potential distance potential difference is this right here that they add up okay so they add up so I'll come back to that the other thing that we'll need here is Ohm's Law because it's talking about resistance and the potential difference so that's the other thing we'll need so let me write those down in my space here so first Ohm's law and then secondly for series that the voltages add up Okay so it's asking for if several resistors are connected in series in an electric circuit the potential difference across each resistor so what that looks like is you have a whole bunch of resistors connected like this okay in series so it wants to know what's their potential difference of that what's the potential difference of that what's the potential of it and what's the potential difference of this so in that case let's rearrange this formula to solve for potential difference which will be V equals i r so that's what we're going to substitute in for each one of these V's so V1 is going to be i1 times R1 V2 is going to be I2 times R2 and V3 is going to be I3 times R3 and so on so what this means is the answer is Choice One it varies directly with the resistance of each resistor so V is directly proportional to R and that's shown here by uh Ohm's law okay for number 30 number 30 says in medium X light with a wavelength of that many meters travels at 2.20 times 10 to the 8 meters per second in medium why this light has a wavelength of that what is the speed of light in medium why okay cool so for this question 30. let's write these things down let's say I'm gonna do one and two so for medium one this will call medium y medium X sorry and for two we'll call medium y so let's write down these variables it says medium X the wavelength is that so wavelength of medium X is 3.44 times 10 to the negative seven meters and it travels at a speed of 2.2 times 10 to the 8 meters per second so that's that and then in medium y this light has a wavelength of that so in medium y the wavelength is different it's 3.12 times 10 to the negative 7 meters and we don't know what the speed of light is in that Medium that's what we're going to be solving for okay so for this one um what we need to do is go to our reference table and we need to see if there's a formula that involves two different wavelengths and two different speed of light so let's bring up the reference table with waves that's page five and the formula that we need is this one right here but we don't need all three parts we actually just need speed of light and wavelength so let me write that down we have a ratio V1 over V2 equals Lambda 1 over Lambda 2. okay so I called medium x one so we'll just put a 1 here and a 1 here and I called medium y two so we'll just put a 2 here and a 2 here so we'll just do our substitution but before we do that let's make sure that we're solving for v2 first so in order to do that I'm going to cross multiply so Let's cross multiply okay so we'll cross multiply so V1 times Lambda 2 is V1 times Lambda 2. and V2 times Lambda 1 is V2 times Lambda 1. I'm solving for v2 so I'm going to divide by Lambda 1 on this side that cancels that out divide by Lambda 1 on this side and I'm going to be left with V2 equals V1 times Lambda 2 over Lambda 1. so the speed of light of medium x times the wavelength of medium y divided by the wavelength of medium X okay so the substitution looks as follows we have 2.20 times 10 to the 8 meters per second I'll put this in parentheses and we're multiplying by the wavelength of medium y so we got three point twelve times 10 to the negative 7 meters and we're dividing that by the wavelength of the wave in medium X which is 3.44 times 10 to the negative 7 meters okay again since we're multiplying and dividing everything I'm going to notice here that I have uh 10 to the negative 7 here and a 10 to the negative 7 here so I'm just going to cancel this out to simplify my calculations so it gives me what I'm going to put into my calculator is 2.20 times 10 to the 8 times 3.12 and then that whole thing is divided by 3.44 and this should give me meters per second so let's see if we get an answer so let's pull up this calculator we're going to do 2.20 um I'm going to do my shorthand notation so times 10 to the 8 times 3.12 and then divide that by 3.44 I got a really really large number okay so let's see if I put it in scientific notation if that changes anything so parentheses 2.20 times 10 to the 8 close the parentheses we're going to multiply by 3.12 and then divide that by 3.44 same answer okay so let me write down this whole number we have 1 9 9 5 3 4 8 8 3.7 if I move this decimal over one two three four five six seven eight we got 1.99 times 10 to the 8 which is approximately 2 times 10 to the eight so that ends up being our answer after all that answer is that all right for 31 it says a nuclear reactor produces this many joules of energy per year how much mass is converted to energy by the reactor in one year so it gives me energy 2.7 times 10 to the 16 joules how much mass is converted Mass so on the reference table let's bring up the reference table where still on page five the only formula that we can use really is going to be this formula this is the energy Mass equivalence and so what this is is it means that energy energy can convert to Mass and mass can convert to energy you'll notice that the formula requires the speed of light so E equals m c squared We need c on page one of the reference table has C which is the speed of light that's this value so let's write that down let's do the substitution so we have oh actually we don't want to do that substitution yet because we need to solve for Mass so let's solve for mass and this is going to be a simple one we're just dividing by c squared on both sides so mass is equal to energy over c squared so that looks like 2.7 times 10 to the 16. divided by 3 times 10 to the 8 and then this term is squared so in my calculator let's see what this looks like we have two point seven times 10 to the 16. and we're dividing by three times ten to the 8 and 3 times 10 to the 8 is squared so this gives me a whopping mass of 0.3 kilograms a lot of joules of energy for a little bit of mass this gives us answer Choice One for 32 32 says the diagram below shows the initial charge and position of two identical conducting spheres on insulating stands if the series are brought into contact with each other and separated sphere B will have a net charge of blank and then we got a whole bunch of positive and negative values so for 32 when conduction occurs conduction is you're going to have the charge of the first object plus the charge of the second object and it's divided by two and this is going to be the charge on each new object so that's going to be negative 7 times 10 to the negative 6 coulombs plus three times ten to the negative 6 coulombs divided by two and let's put this in the calculator we'll have negative seven times ten to the negative six plus three times ten to the negative six and this whole thing is divided by two we end up with an answer of negative two times ten to the negative six coulombs so something set up with the calculator is this button here means minus subtraction and this button here means negation so negative so you use this one you want to put a negative um sign in front of a number and you use this button when you want to subtract two values so just be careful because sometimes you'll get errors if you switch the two all right so in this case the answer is choice 2. for number 33 number 33 says an anti-muon neutrino is okay let's write this down anti muon neutrino let's bring up my reference table when dealing with muons and anti-muons and all that this is Page Three so here we see there's a muon neutrino right here and this is under lepton so a muon neutrino is a lepton okay and it has a charge of zero zero Elementary charges so that's the charge equals zero for anti-particles it has the opposite charge so the opposite of zero is zero so the answer here um is going to be choice 2. lepton with a zero charge all right for number 34 number 34 has two waves and we're supposed to figure out what the superposition is so it says the graphs below show the displacement of a certain particle in a medium versus time due to two periodic waves and be traveling through the medium the superposition superposition of the two waves will cause the particle of the medium to have a maximum displacement of blank okay superposition superposition means adding waves this is when the waves add up this is basically another thing for interference okay I'm gonna give a little cheat here so it's it's basically interference so in this case what we're gonna do is we want to look on the wave and we want to see what these maximum displacements are so we can figure out the new maximum displacement so the maximum displacement for wave a occurs here whoa not a parallelogram which is at two so for a it's two meters and the maximum displacement for wave B happens at three three meters so the displacement for B equals three meters so the new displacement is going to be a plus b that's the superposition that's going to be two meters plus three meters and that's simply five meters so that is Choice four so the scary part of this question is the word superposition for number 35 number 35 says the diagram below represents a wire that is not part of a complete circuit just above the poles of two magnets moving the wire downwards between the poles and the direction shown the diagram well one induce an alternating magnetic field between the poles of the magnets to induce a potential difference between the ends of the wire three decrease the wire's resistivity or four reverse the direction of the magnetic field Okay so let's do a process of elimination here first of all the wires resistivity cannot change unless you change the wire so the wire is not changing so there's no change in the resistivity secondly reversing the direction of the magnetic field this most likely won't happen unless you change the direction of the magnets so the magnets aren't changing so the direction of the magnetic field shouldn't change all right so then we're left with one and two so one it says induce an alternating magnetic field between the poles of the target of the magnets this is also wrong and I think this would induce my um attempt some students that study these types of questions because when you move um for 35 um the the whole idea is Electro magnetic induction and electromagnetic induction basically has to deal with um moving electric fields will create magnetic fields and moving magnetic fields will create electric fields that's because when you move a magnet current will um start flowing through any conductors and when you start moving the electric field a magnetic field gets created so this word induction induced I see that it's here so I might be tempted oh that's probably the whole thing but make sure you read the whole question um and all the answer choices before making your choice so the answer is induce a potential difference between the ends of the wire so the potential difference it means you have a low voltage here and a high voltage here potentially or a positive voltage and a negative voltage that is a potential difference the difference of potentials so um the answer is 2. all right so that concludes section a section a um a lot of multiple choice questions let's get through these remaining parts of the exam so this is now part B1 is 36. 36 says which graph best represents the motion of an object traveling at constant positive velocity constant positive velocity so constant velocity means no acceleration if there's no acceleration if we look at this um formula on the reference table this one let's copy this question this formula down okay if there is no acceleration this term equals zero so we can rewrite this equation as D equals initial velocity times time this is a function of distance or displacement as a function of time so that means that we can graph this is on the y-axis and T is on the x-axis so time and displacement if we were to graph this we would get a nice straight curve like this because it must be positive since the problem says positive so the answer is that just one number 37 number 37 says a cannon ball is fired with an initial velocity of 100 meters per second at an angle of 15 degrees above the horizontal what are the horizontal VX and vertical v y components of this velocity so we're being asked to figure out VX and v y horizontal and vertical components okay the other things I'll also include is the initial velocity which is 100 meters per second and Theta which is 15 degrees so let's bring up the reference table we're looking at these two formulas here these have to do with vectors these are General um equations for figuring out the components of a vector so if you have a vector that is pointing in some direction there is going to be a horizontal component that makes up that vector and there is going to be a vertical component that makes up that vector so this is v y and this one on the horizontal is VX so we can use those formulas let's rewrite them we have a x equals a cosine Theta and a y equals a sine Theta in this case instead of a we have V and instead of ax we have VX instead of a y we have v y so replacing those we have VX equals V cosine Theta and v y equals V sine Theta substitution looks as follows now if I look at this before I move forward let's trigger the reference table if I look before I calculate both of these I actually need to calculate 1 because I can see based on the answers all of the V X's are different 96.6 25.9 76 and 65. so I only need to calculate VX and once I get my VX it's going to be correct I'm going to calculate both in this case to show but um sometimes you can save time on the test just need to calculate one so here VX is going to be equal to V which is 100 meters per second times cosine cosine is a function 15 degrees is what we're substituting so here's what the calculation looks like before I do my calculating I want to make sure that the mode in my calculator is in degree mode so I can see here that it's not it's in radians so I want to change this to degrees you can change the mode of your calculator by clicking mode and then changing what uh parameters you need to change and then you can exit out of this by clicking second mode to quit okay so I'm going to do 100 times cosine of 15 degrees and that gives me 96.59 let's write that down 96 I'm going to round this to 6 meters per second so if I look here that gives me Choice 1 is the answer for VX if I do the math for v y we'll do 100 meters per second times sine of 15 degrees and this will give me 25 point nine meters per second Tas need to answer your question about when do you change it um you when you're taking the physics regions always keep it in degree mode so all the equations use degrees that involve sine cosine on the reference table you'd maybe change it back to radians if it's your own personal calculator if you're in like an algebra class okay so for 38 it says a 1200 kilogram car is moving at 10 meters per second when a braking force of 3000 Newtons is applied how much time is required to bring the car to rest okay easy one let's write out our Givens we have a mass of 1 200 kilograms it's moving at 10 meters per second so that's our initial speed initial speed is 10 meters per second when a braking Force so it's breaking so I'm going to apply a negative Force here so negative 3 000 Newtons it does not indicate that it's negative but that word breaking means that it's an opposing Force how much time is required to bring the car to rest so bringing the car to rest means that the speed is zero meters per second bring to rest means the final speed is zero so the end the the unknown here is time according to our reference table we need to combine two formulas okay we need to combine this formula the impulse formula and our momentum formula so let's write those down we have I don't need to I'm going to write down the whole thing here but F net times time equals Delta p and also P equals mass times velocity okay all right so for this we actually don't need J we just need this section so let me rewrite that we have fnat times time equals Delta P recall that Delta p is equal to final momentum minus initial momentum and if momentum equals mass times velocity final momentum is going to be mass times final velocity and initial momentum is going to be mass times initial velocity now since final velocity is zero this term here cancels out so we can rewrite and this is all that's left so we can rewrite this formula to F net times time equals Delta p is now negative MV so negative mv1 v i and we're solving for time so I'm going to divide by net force on both sides so time equals negative m v i over uh F net this substitution looks like this so 1200 kilograms times initial velocity is 10 meters per second and the force is negative three thousand foreign so let's put this into our calculator so we have negative 1200 times 10 and we're dividing by negative three thousand and we get a simple four let's see equals four and the answer is T equals four seconds that's Choice four all right for number 39 number 39 says which graph best represents the relationship between speed of light and a transparent medium and the absolute index of a fraction of that Medium so for question 39 we're relating speed of light this is by the way speed of light in a vacuum speed of light in a medium so uh it represents the speed of light in a transparent medium speed of light in the median is V so this is speed of light in a medium and N is the absolute index of refraction okay let's bring up our reference table reference table with absolute index of a fraction that's page five let's write down this formula we see here so that is n equals c over V we need this formula because what we need to see here on these graphs this is our y-axis okay and this is our x-axis so on a graph is our y-axis this is our x-axis we graph things with the Y on the left side of the um equation and X is usually on the right side so if we're going to graph this function y equals x this is what the graph looks like so we need the similar thing here so if we see that on the graphs the speed of light and the medium is on the Y so that's this we need to place this as our y variable and we need to get that over here but n which is actually on the x-axis since the absolute index of refraction we need to move that to the other side so let's cross multiply this we'll get n v equals c and then we're going to divide by n so dividing my n will give us V equals c over n okay so now we have this in the form of y equals some constant over X okay so this is the form of the graph we're looking for which is Y equals X inverse um let me just double check that that is the correct answer yeah that's the correct answer cool that's Choice One all right for number 40 it says A student uses a string to whirl a 0.25 kilogram mass and a horizontal circular path that has a 0.80 meter radius if the magnitude of the centripetal force exerted on the mass with the string is 25 Newtons what is the speed of the mass so speed of the mass let's write out all these variables so we have Mass equals 0.25 kilograms we have radius 0.80 meters we have the centripetal force is 25 Newtons centripetal force is 25 Newtons and it wants to know what the speed is so let's see if there's any formulas that look like this so centripetal force is on the last page of the reference table and I'm seeing these two formulas both of these formulas let's copy down we'll have to rewrite them so FC equals m times AC and AC equals V squared over r okay so I need to solve for V I'm going to combine both of these formulas so I'm going to take um I'm going to take acceleration and substitute it into here okay so this is what that looks like it looks like FC equals m times V squared over r that's the substitution now what I can do I have a formula with all these variables v f r and m I'm going to rearrange this to solve for V so we're going to cross multiply this is going to give us f c times R equals m v squared then I'm going to divide by m so that's going to be FC times R over m and then I'm going to take the square root on both sides so taking the square root on both sides we will get radical f c times R over M and this is equal to our velocity so this is the formula that I want to use as I'm substituting so let's rewrite this formula and use a different color so V equals the square root of FC times R over M and let's substitute okay so FC is 25 Newtons R is 0.80 meters and M is 0.25 kilograms let's put this in the calculator we're going to do square root of 25 times .80 divided by 0.25 and that gives us eight point nine four meters per second let's see if that is a answer Choice 8.9 is close so we'll use Choice two number 41 says a deuteron is formed by combining a proton and a neutron the mass of the deuteron is 2.39 times 10 to the negative 3 Universal mass units less than the combined masses of a proton and a neutron this Mass difference is equivalent to so let's write down it says the mass is equal to 2.39 times 10 to the negative 3 Universal mass units Universal Mass units this is not kilograms so oftentimes when you see something you're maybe unsure of it's a good place to go to the reference table let's go to page one of the reference table and let's see if we have anything about this Universal mass unit I see here it says one universal mass unit is equal to this number so let's write that down so one Universal mass unit U is equal to 9.31 times 10 to the two m e v Mega electron volts that's what that stands for so that's what one Universal mass unit is so in order to figure this out if I need to figure out what this Mass difference is equivalent to the the problem is really set up um with some confusing vocabulary uh with this whole difference you might be thinking oh maybe you need to subtract something no all you need to do is multiply these two numbers because this is what the mass is that you're trying to figure out and convert and this is what 1 equals so you need to convert this number this Universal mass unit said it's in the problem to this unit so you just multiply the two so you're going to do 2.39 times 10 to the negative 3 Universal mass units that's the thing and you're going to multiply this by this number so this is 9.31 times 10 to the 2 Mega electron volts per Universal math unit per one so let's put this in the calculator you're gonna get 2.3 times oh 2.39 oops 2.39 times 10 to the negative three times 9 point 3 1 times 10 to the 2 and we get 2.225 let's write that down 2.22509 and the units are Mega electron volts since the U's will cancel out so this is what our answer is but if we look 2.23 is the closest answer so that's going to be our answer next number 42 number 42 is kind of another one designed to like trick people up so number 42 says a gravitational force of magnitude F exists between Earth and a satellite on Earth's surface so when it's on Earth's surface it equals F the satellite is sent into orbit at a distance of three Earth radii above Earth's surface as shown in the diagram below so R represents the radius of Earth 3r represents three times the Earth's radius above the surface of the Earth what is the magnitude of the gravitational force between the Earth and the satellite when the satellite is in orbit okay so we're reusing that formula that I'm sure looks familiar this comes from page six of the reference table just for reference right here okay so we're using that and the only reason why we need to use this is for that the relationship between F and r squared okay so initially it's saying so on um the surface of the planet f is equal to G M1 M2 over capital r squared okay so we're replacing the r in the diagram with little r and we're replacing f e with f from the problem okay so that's on the surface in orbit this is no longer just F okay so I'm going to put f but there's some blank number that needs to go in front of this right you'll see in the answer choices it's either 1 over 16 1 over 9 3 or F or four so now what we're going to do okay so sorry about that so now what we're going to do is we're going to rewrite these variables and we need to figure out what goes here is it three or something else well it's something else because R is measured from the center of the planet to the surface so 3r is measured from the surface to the orbit so this is not the real distance it's actually 3r plus r which is 4 R make this a different color so this is 4r actually so four r squared ends up being 16 on the denominator so that means we need to have a 16 on the denominator for our F which gives us Choice One all right 43 43 is another one that might trip you up because you could get like two possible answers so for but only one is correct this one says as part of an investigation on quantization a student measured and recorded the mass of five identical containers each holding a different number of pennies the table shows the students data based on the data what is the most likely mass of one penny okay so we'll see 3.2 grams 6.4 grams 9.6 grams 12.8 grams and what we want to do here is we need to look for numbers that are similar so this number here and this number here are similar so let's write them down we got 35 oops okay whatever 30 I keep putting 3.5 .2 grams and we have [Music] 38.4 grams if we subtract these two let's see what we get in the calculator just to make sure so 38.4 minus 35.2 gives us 3.2 okay so let's put 3.2 all right let's look at another similar value so we got 46 uh 41.6 and 48. let's subtract those two okay so let's do 48 grams minus 41.6 grams when we do that calculation 48 minus 41.6 we get 6.4 all right so which one is it these are most likely all whole pennies okay and it says based on the data what is most likely the mass of one penny so it's not possible that from container one right here's container one and then here's container four that's what we just compared uh in the first uh section this is container one this is container four it's not possible that there's a half penny here and then a whole Penny uh between containers three and containers five okay what's more likely is this value here represents two pennies and this value here represents one penny so the answer here just by some I guess like basic logic after subtracting is uh Choice One all right for number 44 which graph represents the relationship between frequency and period um so for 44 we're trying to figure out how frequency is related to period so if we look on the reference table it gives us the answer so let's look at frequency and period frequency and period are right here they're inverses so frequency and period are inverses so the only graph that shows an inverse relationship is Choice four number 45 number 45 says what is the current in a conductor if this many electrons pass a given point in the conductor in 10 seconds so we have the number of electrons so number of electrons equals 3.15 times 10 to the 18 electrons we're going to use e Elementary charges for electrons and it says the time is 10 seconds we're being asked for the current according to the reference table page four says that current is equal to the charge divided by the time so current equals charge divided by time however we did not we're not given the charge we're given the number of electrons in elementary charges so this here is the charge of the electron in elementary charges so we need the charge of the electrons in uh coulombs so bringing back up this reference table and going to page one it tells us that the elementary charge is equal to this many coulombs so this is saying that one electron equals 1.60 times 10 to the negative 19 coulombs so we have this many electrons and that many electrons is going to be equal to that number times uh this number so in the calculator let's bring up the calculator we're going to have 3.15 times 10 to the 18. and we're going to multiply that by 1.60 times 10 to the negative 19. and we got 0.504 coulombs so this is the charge that we want to use so this is what Q equals so let's substitute that in we get 0.504 coulombs divided by 10 seconds if we're dividing this by 5 we just move this decimal place over so this is going to be 0.0504 amperes and that gives us Choice One for number 46 number 46 says a particle with a charge of positive three Nano coulombs is placed in an electric field excuse me with a magnitude of 1500 Newtons per coulomb what is the magnitude of the electrostatic force on the particle okay so let's write this down so 46 we have charge equals positive 3 Nano coulombs Nano coulombs needs to be converted according to our reference table Nano is this right here so we're going to replace Nano with times 10 to the negative 9. coulombs so that's what that equals next part of the problem says is placing an electric fill with a magnitude so the electric field has a magnitude of 1500 Newtons per coulomb what is the magnitude of the electrostatic force let's go back to the reference table to figure out what formula we need to use so we're on page four and we see this formula right here electric field charge and electrostatic force so let me write that down so we have the electric field equals the electrostatic force divided by the charge so what I want to do is I want to solve for the electrostatic force so the electrostatic force is going to be equal to the electric field times the charge and this looks like this this is the substitution so e is 1500 Newtons per coulomb and Q is this so 3 times 10 to the negative 9 coulombs and uh calculator this is what this looks like so 1500 times three to the negative nine and we get 4.5 times 10 to the negative 6. since this is a force it's measured in Newtons 4.5 times 10 to the negative 6 is Choice One all right almost done the multiple choice yay this is a long very long stream okay 47 says the graph below represents the motion of an airplane that starts from rest and takes off from a single from it takes off from a straight Runway which quantity is represented by the slope on the graph this one's a very easy one so slope is equal to your y-axis divided by your x-axis so on the y-axis we have velocity this is your y-axis and on your x-axis you have time so a formula velocity divided by time if we check on our reference table velocity divided by time is this formula right here so that's acceleration this equals acceleration so the slope of a velocity versus time graph is equal to acceleration for number 48. 48 says diagram below represents two horizontal platforms that are at different heights above level ground A ball rolls off the taller platform with a horizontal speed of 15 meters per second travels through the air landing on the top of the shorter platform what is the total time the ball is in the air total time the ball is in the air solving for total time okay so in order to solve this let's use a formula on the reference table okay first before we figure out what formula we need to write down what variables we have we have V uh it says it rolls off with a horizontal speed so horizontal speed this is our initial velocity the X direction is 15 meters per second we remember that the acceleration in the X direction is zero and the other thing that we have are some vertical variables so the vertical variables in the y direction since this object is uh assumed to be on air we're talking about neglect friction is going to be negative 9.81 meters per second squared the initial Vertical Velocity is zero meters per second since it rolls off horizontally initially there's no vertical motion of it so initially it's going to be zero there's also a vertical distance and that distance there's a difference here that is equal to six meters minus 3.6 meters six minus 3.6 equals 2.4 so this change in vertical height is 2.4 meters something to note is when we're doing these types of problems where we have horizontal motion and vertical motion you can't mix your variables together in the formula that we're going to pick so we're solving for time we have some initial speed in the y direction in the X direction we have our accelerations the X and Y Direction and we have a distance in the y direction so let's bring up our reference table and let's see if we have any very linear formulas that we can use we could use this formula here same formula that we used a while back we could use this to solve for our time so let's write that down we have D equals v i t plus one half a t squared now these are all y variables so I'm just going to replace these as a d y equals v i y t plus one half a y t squared another thing to note is because our velocity is zero this becomes zero so we have DUI equals one half a y t squared if I solve for t using some algebra we're going to get T equals the square root of 2 times d y over a y in class this might have looked like 2 H over G okay that's what that might look like so let's plug this into our calculator so we're going to do the square root of 2 times the height difference which is 2.4 and we're dividing by 9.81 and we get a time of approximately 0.70 seconds which is choice three all right moving on last two multiple choice questions 49 says four mechanical waves are created in the same medium over the same time interval Which diagram represents the wave that transfers the greatest amount of energy greatest amount of energy for mechanical waves is going to be related to the amplitude so we'll say that is approximately equal to that and for electromagnetic waves what's related to the energy is the frequency okay so we're looking for the one with the greatest amplitude so that is going to be Choice two for number 50 Which diagram represents a light Ray increasing in speed as it travels from one medium to another so this has to do with refraction okay so more bending away from the normal line means increasing speed so we're looking let's look at each choice here so Choice one has this angle as it comes in and then it has this angle as it goes into medium a that's a decrease in angle so it's not Choice One so we want well when I said more bending I'm sorry I was unclear when I said more bending it means increase in Theta so you can conclude that uh when you increase Theta you then increase the speed here's another case the angle here decreases this is the only example here where the angle increases so we're going to use choice three we're going to use choice three here okay so that wraps it up for the multiple choice questions so now what I want to do is move on to the the um oops move on to the short answers okay now when it comes to the short answers your short answers you have to show work for some of the questions so this is the answer booklet from last year uh and then when you guys take the regions there will be um this answer book so there's space to show your work and then you'll notice here that for this like for number 53 you don't have to put your unit in your answer so you only have to put your units when you substitute so let's see if we could go through these quickly so I can go to sleep okay so for this 51-52 that's this part right here so 51-52 says to charge a cell phone battery 3.69 times 10 to the three coulombs of charge is moved through a potential difference of 3.7 volts calculate the maximum amount of electrical energy gained by the battery so all we're concluding equations as a substitution okay so let's write down my variables okay so we have charge which equals 3.69 times 10 to the 3 coulombs we have a potential difference of voltage equals 3.70 volts and calculate the max amount of electrical energy gained so that would be w for electricity W is our energy variable so this is the unknown so let's open up the reference table page four on the reference table has this formula this is a different color because this formula that's what we want to use so we're going to use V equals W over Q we're going to cross multiply so that way we can get W equals V times Q and then that's the formula that we're going to use to substitute so w equals V which is 3.70 times Q which is 3.69 times 10 to the three coulombs and actually that's all you need to show in terms of the work to get full credit um the stuff that I haven't read uh so but I'm gonna continue so this is in the calculator it's going to be 3.7 times 3.69 times 10 to the 3 and we get thirteen thousand six hundred and fifty three okay so that's a lot and the units here in case we forget that it's joules we can multiply volts times coulomb so volt coulombs would be the answer which is equal to 1000 13 653 joules now realistically what you should be doing is putting this in scientific notation so in scientific notation this would be one point three seven times ten to the four joules that's our answer okay for number 53 number 53 says determine the magnitude of the weight of the oh and just to clarify this is where the points you would get so this here would be one point for 51. and one of these answers here would be the other point for 52. 53 says determine the weight the magnitude of the weight of the ice skater um oh and that's based on this problem here so a 55 kilogram ice skater slides across oops let's get rid of the calculator 55 kilogram ice skater slides across a level surface of ice and the force of friction acting on the skates has a magnitude of 11 Newtons determine the magnitude of the weight of the ice skater so magnitude of the way the ice skater weight is FG times mg and for this problem you don't need to show any work since it's just one point but the mass is 55 kilograms and the weight um the acceleration due to gravity is 9.8 meters per second squared and once we get this that's 55 times 9.81 is approximately 10. so you get 550 Newtons another acceptable answer is 540 Newtons okay so either one of those answers are acceptable so if you put 9.81 you'll get 539 point something and if you round it to 10 you'll get 550 approximately all right for 54 to 55 it says calculate the coefficient of friction between the ice skater and the ice so coefficient of friction this formula is on the last page of the reference table that has a coefficient of friction there's only one formula on the reference table as the coefficient of friction it's this so let's write that down so we have friction equals coefficient times the normal force now since this ice skater is on a level ice surface that means that the normal force is equal and opposite to the weight so we can replace uh we can do that replacement like that and then we rearrange this solve for the coefficient of friction coefficient of friction is going to be friction divided by the weight our substitution is going to be 11 Newtons that's from the problem 11 Newtons is the force of friction and the weight is from our previous problem so my answer was 550 so I'll do 550 Newtons 550 Newtons and let's see what we get here when we calculate this we got 0.02 no units because the units cancel out so that's the answer for um 55 so this right here is the point for 55 and this right here is the point for 51. just this section part okay let's move on so the next one says base your answers to questions 56 and 57 on the information and diagram below and on your knowledge of physics a student produces a wave in a flexible spring stretched along a tabletop by shaking one end of the sprig at a frequency of 2.0 Hertz determine the amplitude of the wave produced in the spring so the amplitude of the wave producing the string of the spring here if we have a line that kind of separates are positive and negative sections here then this is our amplitude and since the total thing total um measurement is one meter half of that is our amplitude so we get 0.5 meters we don't need to put the unit since the unit is already here on our answer booklet for 57 determine the wavelength of the produce of the of the wave produced in the spring so for wavelength wavelength is going to be the total distance or length that we have divided by the number of um let's say Cycles okay so total distance is 4.5 so 4.5 meters and the number of Cycles we have one cycle that's one we have two and we have three so that's three Cycles so we're going to divide by three so calculator 4.5 divided by three is one point five so we'll put 1.5 again we don't need to put the units because we have the unit there on our answer booklet again no work is needed to show 56 and 57 it can all be done in your calculator 58 scroll down to 58. 58 says um 58 to 60 are together so it says a 100 Newton box is pulled up pulled up a 20 meter long incline by a constant force of 80 Newtons the vertical height gained by the box is 10 meters determine the total work done in joules by that 80 Newton Force pulling the Box up to the top of the incline so total work done total work done in joules by the 80 Newton Force so we're talking about the force pulling it up to the top so let's look at a reference table work is this formula right here so work equals force times distance so let's write that down work equals force times distance now the force and the distance have to be parallel that's a note so Force and displacement we'll call it have to be parallel so if our force is this way our distance that we're looking at is also this so we're looking at that so that happens to be pretty simple pretty simple calculation work equals 80 Newtons times 20 meters eight 80 times 20 is 1600 so 1600 and Newton meters but we can see that our units here are joules so this is 1600 joules so we'll put 1600 joules as our answer for 59 determine the total amount of gravitational potential energy in joules gain by the box as it's pulled to the top of the incline for gravitational potential energy gravitational potential energy is this formula gravitational potential energy is mg times Delta h let's write that down gravitational potential energy equals mg times Delta H in this case Delta h is 10 meters and mg is 100 Newtons so mg is 100 Newtons Delta H is 10 meters this is 1 000 newton meters or 1000 joules so we'll do one thousand joules number 60 says explain why there's a difference between the total work done by the 80 Newton force and pulling the box at the top of the incline and the amount of gravitational potential energy gained by the box as it was pulled to the top so they're asking to explain why is there a difference between 1 600 joules and 1000 joules and you have various answers you can say because of friction you can say um there's some kinetic energy you can say there's some Heat or thermal energy or internal energy or other energy present only pick one of these okay don't include all three you'd only pick one if this was your answer all right next block of questions involve the circuit the diagram below represents an electric circuit consisting of 110 Ohm resistor and a 220 Ohm resistor connected to a source of potential difference calculate the equivalent resistance of the circuit show all work including equation and substitution so for the 61 part we're using the formula formula is going to be 1 over actually let's double check the formula so this is a parallel circuit so the formula that we need to use for equivalence resistance is right here so we'll write down one over the equivalent resistance equals 1 over R1 plus 1 over R2 I'll stop at R2 since we only have two resistors the next thing to do is to do a substitution so 1 over r e q equals 1 over 110 ohms units plus 1 over 220 ohms remembering our units so that right there is your um point for 61. okay your substitution now to continue this let's put these in the calculator so I'm just going to bring this work up here 1 over req equals so 1 over 100 let's put that in the calculator one divided by 110 is 0.009 something something and then we're going to divide 1 divided by 220. and that is 0.0045 okay so now what we're going to do is we're going to add those two together so add the point zero zero nine o nine etcetera Etc could have just put in the fractions right the alternative would be to do this one divided by 110 Plus 1 divided by 220. and what we get is 1 over R equivalence equals 0.013636 repeating okay oops so this is not the answer so in order to get the answer we actually have to take the inverse of that so the inverse if we bring back up our calculator we're going to do 1 divided by this answer so we'll put second minus sign which give us our answer and that gives us 73.3 so our equivalence equals 73.3 ohms the math involved to do that is you raise this side to the negative 1 and you raise this side to the negative one so you could put in in parentheses 0.013636 repeating and then you raise that to negative one and you get the same answer okay so that's what you would do all right and this right here is your point for 62. for 63 64 it says calculate the total current in the circuit total current in the circuit is going to be equal to this equation using Ohm's law so let's write that down total current uh well let's write down R equals V over I and then we'll rearrange this to be I equals uh V over r now for total stuff total quantities we want to utilize the total voltage divided by the total resistance so total voltage is the voltage of the circuit which is 6 volts so that's 6 volts and the total resistance is what we calculated up here in the previous part so 73.3 ohms so 6 divided by 73.6 73.3 so 6 divided by 73.3 that gives us 0.081 eight five dot dot dot and peers or if we forget that um current is measured in amperes you would say 0.082 We'll round that volts per coulomb so volts volts per ohm this is also equivalent okay for 65 65 says compare the power dissipated by the 110 Ohm resistor to the power dissipated by the 220 Ohm resistor so for this one again we're going to bring up the reference table power dissipated is going to be here now we have a few options that we can think about so we want to look for what variables we have we have the resistance we also have the voltage and we have the current so what we can say is let's let's hide this for a second so we have the 110 Ohm resistor and the 220 Ohm resistor so we need to use one of these formulas that has the um resistance uh uh in it so we're going to be this one or this one I think it would be easier to use um uh uh I think it would be easier to use this one because the reason for the parallel circuits parallel circuits have the voltage all equaling the same so if we look at that relationship so power equals V squared over R since it's the same voltage across the the whole thing so for the first resistor it's going to be 6 divided 6 squared divided by 110 ohms and then for the second resistor it's going to be 6 squared divided by 220. and according to this we can say that the power dissipated I spell that right dissipated dissipated by the 110 Ohm resistor is greater than the 220. okay because 36 divided by 610 um 110 is greater than 36 divided by 220. All Right Moving On part C this is the last part of the regions it says for 66 through 70. a group of students constructs a catapult that launches a ball at a Target placed on a lab bench so since measure 0.80 seconds from the time the ball is released until it strikes the target located a horizontal distance of 2 meters from the release point the ball reaches a maximum height of Point P which is 0.80 0.78 meters above the ball's release point the target is at the same height as the release Point neglect friction 66 to 67 says calculate the horizontal component of the ball's initial velocity so horizontal component if we um want to calculate the horizontal component of the falls velocity that formula we can use is distance over time so we can use this since there's no acceleration in the X Direction so distance horizontal distance is 2 meters and time is the total time which is 0.80 seconds 0.80 seconds so this is 2 divided by 0.80 and you get 2.5 meters per second so that's number 66 and 67. four calculate the vertical component of the balls initial velocity initial velocity for the vertical components so we need to figure out the vertical component that's unknown we know that at the Peak here the velocity in the y direction is zero so we can say zero there we can also say that the acceleration in the y direction is 9.81 meters per second squared and we know the distance in the y direction at that point is uh 0.78 meters only thing missing here is time so we actually don't need the time however because we can use the formula from the reference table which is this formula this is found on page six okay so we can use that so let's see so vfy is zero so we can get rid of that v i y is what we're solving for two is just a coefficient we'll just bring that down a is 9.81 and D is 0.78 meters so in this case we want to make sure that we substitute negative here because if not we're going to run into some issues so let's simplify this we got zero equals v i squared and then according to the calculator we have 2 times 9.8 0.78 and that gives you negative 15.288 and then we're going to bring this over to the other side so this is 15.288 equals v i squared and then we take the square root on both sides so that's the square root of that answer there we go 3.9 meters per second equals VI all right so that's 69. next question on your answer booklet draw an arrow originating at a point P that represents the direction of the ball's acceleration at Point P so acceleration at Point p is downward this is the acceleration due to gravity there's no acceleration in the y in the X direction there's only acceleration in the y direction okay this next block of questions 71 to 75 deals with springs it says a spring with a spring constant of 2600 Newtons per meter is compressed 0.10 meters from its unstretched position the spring is released propelling a three kilogram block along a horizontal frictionless surface the block is then it collides with a stationary one kilogram block the block remains joined and they move together as shown in the diagram below so to go over what just happened and what was just red spring is compressed initially then what happens it's released the oh this calculator is in the way so spring is compressed then it's released that energy is converted it this is what it looks like before the Collision this three kilogram block then it collides with the one kilogram block they both stick together and they move together so this is a key term move together indicating this is an inelastic collision so let's go to question 71. question 71 says determine the total amount of elastic potential energy stored in the spring when the spring is compressed so elastic potential energy which is right here elastic potential energy is one half KX squared so let's write that down elastic potential energy is one half k x squared so K it was mentioned K is 1 2 600 Newtons per meter so we'll plug in one half two thousand six hundred Newtons per meter and X is going to be 0.10 meters that term is squared so let's put that in the calculator one-half that's 0.5 times 2600 times .10 squared that gives me 13. answer is 13 joules and that's what I'll put in it's in my answer key here now let me just show something here on the calculator if I put 1 divided by 2 and then I multiply by 2 600. and then I multiply by 0.10 squared I still get the same answer okay so sometimes you can get away with not using parentheses sometimes you can get away with using decimals or fractions just be careful I would err on the side of caution and use parentheses or decimals instead of fractions all right next question uh it says assuming all of the Springs energy is transferred to the three kilogram block calculate the speed V1 of the three kilogram block immediately after it is propelled by the spring so this is saying that all of the potential energy of the spring converts to kinetic energy so on the reference table kinetic energy is this formula kinetic energy equals um one half MV squared okay so potential energy of a spring equals one-half MV squared that's this before and after so now what we're going to do is we need to solve for V since the question asks to determine the speed so we're going to solve for V I'm going to do the algebra really quickly so this is going to be 2 times the potential energy equals MV squared then it's going to be 2 times the potential energy over m equals the velocity squared and then finally it's going to be the velocity equals the square root of two times the potential energy over the mass this is the formula we're going to use we're going to substitute 2 times the potential energy the potential energy was from the previous problem 13 joules and the mass is three kilograms so calculator we're going to do square root of 2 times 13 divided by 3 and we get V equals 2.94 meters per second let me just verify if that is correct yeah cool okay so next next it says calculate the speed of V2 of the two blocks after the Collision so going back to this diagram there is a collision that occurs where the three kilogram block collides with the one kilogram block so this is a situation of momentum the initial momentum equals the final momentum the initial momentum is going to be the mass of that first object times the velocity of the first object it's just one object and then it's going to be equal to the mass of the first object plus the mass of the second object times this new speed okay so this is the before this is the after this is the before this is the after before after so let's write this down in our answer book so initial momentum equals final momentum the first object times the first velocity and if we want to be thorough it's going to be the second object times its velocity but that's zero it's at rest and this is going to be equal to First object plus the second object times the new velocity so we need to solve for that variable there so since this equals zero we have M1 V1 equals M1 plus M2 in parentheses times V2 we can divide by M1 plus M2 okay it just cancels out and we divide by M1 plus M2 and we'll get an answer we'll get a formula of V2 equals m1v1 over M1 plus M2 oh let's bring this up here let's see what that substitution looks like M1 times V1 so uh M1 is three kilograms V1 which is this right here so 2.94 meters per second over M1 plus M2 that's three plus one that's four kilograms so let's put this in a calculator 3 times 2.94 divided by 4 equals 2.2 so V2 equals 2.2 meters per second and this makes sense initially it was moving at 2.9 meters per second it hit something and it slows down to 2.2 great all right this is the last questions 76 says a Mercury atom emits a photon when electron in the atom moves from energy level F to energy level d F to D so initial energy IS F let me write this down actually over here initial energy is f and final energy is d so let's bring up the reference table and this is Page three for mercury we have f which is this value and for d we have this value so f is negative 2.68 electron volts and for D it's negative 4.95 electron volts this formula that we need to use is on page five it's this one the energy of a photon energy of a photon equals the initial minus the final so we're going to put that into our calculator that is the initial is negative 2.68 minus negative 4.95 now we get answer 2.27 electron volts number 77 says determine the energy of the emitted Photon in joules so to convert electron volts to joules there's a conversion factor on page one of your reference table electron volts to joules is right here electron volts to joules so we have one electron volts equals 1.60 times 10 to the negative 19 joules so if we have 2.27 electron volts that is going to be 2.27 times 1.6 times 10 to the negative 19. and and we're going to write down 3.63 times 10 to the negative 19 joules cool number 78 to 79 calculate the frequency of the emitted photon frequency of the emitted Photon we'll need a few things here so page five energy of a photon equals Planck's constant times frequency Planck's constant is on page one of the reference table Planck's constant is right here that's 6.63 times 10 to the negative 34 Joule seconds frequencies what we're solving for and the energy of the photon is what we just got from number 77 so that's 3.63 times 10 to the negative 19 joules this gives us frequency equals and we're going to use the calculator here frequency equals 3.63 times 10 to the negative 19 joules divided by 6.63 times 10 to the negative 34 Joule seconds and so that gives us three point six three times ten to the negative 19. divided by 6.63 divided times 10 to the negative 34. we get 5.48 times 10 to the 14 Hertz is what the unit of measurement for frequency is okay last question last question says based on your calculated value of the frequency of the emitted Photon determine the classification in the electromagnetic spectrum so if our frequency is 5.48 times 10 to the 14. we need to check on the electromagnetic spectrum what that equals so 5.48 times 10 to the 14 Hertz 10 to the 14 Hertz is visible light so we're looking for 5.4 which ends up being somewhere here so green light is what we think it might be so what we'll put down on number 80 is visible light or green so that's the type of photon it is okay three hours later we finish the regions so we actually just finished on time so um hope you guys enjoyed this if you guys have any questions you could reach out to me let me uh I'm gonna end the stream and then you can either comment questions or message me