Edexcel GCSE Physics 1PH0
Key Concepts of Physics
Motion and Forces
Conservation of Energy
Waves
Light and the Electromagnetic Spectrum
Radioactivity
Astronomy
Energy – Forces Doing Work
Forces and Their Effects
Electricity and Circuits
Static Electricity
Magnetism and the Motor Effect
Electromagnetic Induction
Particle Model
Forces and Matter
Motion and Forces
Collisions, and force as the rate of change of momentum
- 3 things to know
- Paper 1
Overview
Momentum in coupling trucks, snooker balls, skaters and a recoiling rifle, force as change in momentum over time, and how crumple zones and air bags lengthen that time.
What you need to know
Answer each one before you reveal it.
A moving snooker ball strikes a stationary one and slows down. Describe the momentum change in this collision.
Explain why a rifle recoils backwards when a bullet is fired forwards.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Two railway trucks collide and couple together. Describe what happens to the total momentum.
Model answer
The total momentum is unchanged, and it is now carried by the joined trucks moving as one.
- 2
A moving snooker ball strikes a stationary one and slows down. Describe the momentum change in this collision.
Model answer
The momentum lost by the moving ball is gained by the ball it strikes.
- 3
Two ice skaters stand at rest and push each other apart. Describe their momenta afterwards.
Model answer
They move in opposite directions with equal-sized momenta, so the total is still zero.
- 4
Explain why a rifle recoils backwards when a bullet is fired forwards.
Model answer
The total momentum stays zero, so the rifle gains backward momentum equal to the bullet's forward momentum.
- 5
A 3 kg trolley moving at 4 m/s collides head-on with a 1 kg trolley moving at 4 m/s the other way, and they stick together. Calculate their velocity afterwards.
Model answer
The total momentum is 12 − 4 = 8 kg m/s shared by 4 kg, so they move at 2 m/s the way the heavier trolley was going.
- 6
State in words the equation that links force, change in momentum and time.
Model answer
Force = change in momentum ÷ time taken.
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