in this problem we'll calculate the average force that a ball will impart to the O to a wall so ball which mass is 2 kilogram is moving with 10 meter per second and it hits a wall and bounces back and it bounces back with a velocity of 8 meter per second and the ball is in contact with the wall for about 20 milliseconds 20 milliseconds that's the time of contact from this information we need to find out what is the change in the momentum of the ball and how much force the ball impacts to the wall and how much force the wall imparts to the ball that's all we will be calculating in this numerical problem and we'll be using the impulse momentum theorem for this in this problem so let's start it this one so we have the given mass of the ball is 2 kilogram and the view 1 that means the the velocity with which the ball is approaching towards the wall and v2 is now when the ball bounces back from the wall and the negative sign the negative sign is because the ball was initially moving in this direction we call this as a positive prediction so anything that is moving in the opposite direction will have the negative sign that's what the negative sign means but it's moving in the opposite direction after bouncing back the time of contact is 20 milliseconds and now changing 20 milliseconds to second so one millisecond is 1 for 1,000 or 1 times 10 to the negative 3 second that's how it changed me into second first let's find out the change in momentum as the name suggests the change means final momentum minus initial momenta so this is the final momentum and this is the initial momentum and when I say the final momentum that means after it bounces back off the wall so how do you calculate the momentum of this ball it should be M times v2 and the momentum here should be M times v1 so M times v2 minus M times V 1 the mass is given 2 and the velocity is negative 8 okay we have to include the negative sign here and minus 2 times 10 so the change in momentum is minus 36 kilogram meter per second okay that's the change in momentum of the ball of the negative sign simply tells you that the final momentum is smaller than the initial momentum or the direction is along the negative x axis now let's calculate the average force if you recall the Newton's second law of motion what is the Newton's second law of motion tell you the Newton's second law of motion tells you the the force acting on an object or the average force is the change in the momentum divided by the change in time okay this is change in momentum change in momentum and this is the time we have calculated the Delta P the Delta P is minus 36 so that is the minus 36 and the time is given right here 20 millisecond or 20 times 10 to the negative 3 second the 20 times 10 to the negative 3 second and the force is now 1800 new ten force the negative eighteen hundred Newton was the negative sign again means the negative sign simply tells you that the that the force is by the wall onto the ball that's the negative sign means and by Newton's third law of motion the ball also imparts force onto the wall so and this force is exactly equal in our budget so the force onto the wall is 1800 Newton and if which is the negative of the average force look at this force so the new positives means the force onto the wall and the negative force means is a force onto the ball port exactly mean the same thing is it has to be equal in magnitude just by the Newton's third law of motion and now let me talk a little bit about why does the ball bounce back so let's say this is the ball here and the ball is moving with velocity v1 and this is after the bouncing back so when it contacts the wall there's a compression onto the ball whatever there's a compression it just behaves like an elastic ball or in other words there is a stool elastic potential energy into the ball because of this compression there's a compression so if there is a compression that means the restore potential energy and the stored potential energy will not change you into the kinetic energy and the kinetic energy happens when it is starts coming out of the wall or movie starts into the opposite direction so this is how the change in internal energy or change from kinetic energy to potential energy again potential energy to kinetic energy so this all embedded in there so think about this one one more time by yourself and again if you have any questions any confusion do not hesitate to contact me okay so this is it for from this video like again do not forget to Like share and subscribe the channel thank you very much