Edexcel Physics A-level: Topic 2 - Mechanics

2.9 - Equations of Motion

• When an object moves with uniform acceleration, use these formulas:
  • v = u + at
  • s = ut + 1/2 at²
  • v² = u² + 2as
• Definitions:
  • s: displacement
  • u: initial velocity
  • v: final velocity
  • a: acceleration
  • t: time
• Example: Stone dropped from 50m bridge:
  • s = 50m, u = 0 m/s, a = 9.81 m/s²
  • Find v using v² = u² + 2as
  • Find t using s = ut + 1/2 at²

2.10/2.11 - Graphs of Motion

• Distance: Scalar, ground covered
• Displacement (s): Vector, overall distance from start
• Speed: Scalar, distance per unit time
• Velocity (v): Vector, rate of change of displacement
• Acceleration (a): Rate of change of velocity
• Graph Interpretations:
  • Acceleration-time graph: Area under graph = change in velocity
  • Velocity-time graph: Gradient = acceleration, Area under graph = displacement
  • Displacement-time graph: Gradient = velocity
• Instantaneous vs. Average velocity

2.12 - Scalars and Vectors

• Scalars: Only magnitude (e.g., distance, speed, mass)
• Vectors: Magnitude and direction (e.g., displacement, velocity, force)
• Vector expression: Bold, underlined, or with an arrow

2.13 - Resolving Vectors

• Calculation: Use trigonometry
  • x = V cos θ, y = V sin θ
• Scale Drawing: Use a ruler and protractor

2.14 - Adding Vectors

• Calculation Method: Use Pythagoras and trigonometry for perpendicular vectors
• Scale Drawing: For other angles
• Components addition for same direction

2.15 - Projectile Motion

• Independent vertical and horizontal components
• Use uniform acceleration formulas separately
• Example: Ball projected at 20 m/s, 60° angle

2.16 - Free-body Force Diagrams

• Show all forces acting on object
• Equal forces imply constant velocity

2.17 - Newton's Laws of Motion

• 1st Law: Object stays at rest or constant velocity without resultant force
• 2nd Law: F = ma, acceleration proportional to resultant force
• Terminal Velocity: Equal driving and frictional forces

2.18 - Gravitational Field Strength and Weight

• g = F/m
• Weight W = mg
• Example: Find acceleration using weight and free-body diagrams

2.20 - Newton's Third Law

• Equal and opposite forces
• Example: Book on a table

2.21 - Momentum

• Momentum (p) = mv
• Conservation principle: Momentum before = momentum after

2.23 - Moments

• Moment = Force x Perpendicular distance
• Principle of Moments: Sum of anticlockwise moments = sum of clockwise moments

2.24 - Centre of Gravity

• Point where gravity acts
• Use plumbline method for irregular objects

2.25 - Work

• Work done (W) = Force x distance in motion's direction
• Adjust for angle: W = F cos θ x s

2.26 - Kinetic Energy

• E_k = 1/2 mv²

2.27 - Gravitational Potential Energy

• E_p = mgh

2.28 - Conservation of Energy

• Energy cannot be created/destroyed, only transferred
• Total energy in a closed system remains constant

2.29 - Power

• Power (P) = Energy transferred / time
• P = Work done / time

2.30 - Efficiency

• Ratio of useful power/energy output to input
• Efficiency = Useful output / Total input