Question 1Warm-upHigher
A 2 kg trolley moves at 3 m/s. Calculate its momentum.
p = m × v.
Worked solution
- kg m/s
Answer: kg m/s
GCSE & IGCSE physics practice
Momentum questions and answers
Momentum is mass × velocity, , in kg m/s. In a collision or explosion, total momentum before = total momentum after (conservation of momentum). The force on an object equals its rate of change of momentum, , which is why airbags and crumple zones work.
8 questions · Higher tier · Every answer is checked as you type it, with a full worked solution. Updated .
Where momentum comes up
| GCSE (AQA) | Higher only. Recall p = mv (Physics and Combined Science). F = mΔv ÷ Δt is on the equation sheet, for GCSE Physics only. |
|---|---|
| Cambridge IGCSE (0625) | Supplement (Extended): recall and use p = mv and impulse = FΔt = Δ(mv); conservation of momentum in one dimension; resultant force = change in momentum per unit time. |
The method
- p = m × v. Direction matters: give velocities in one direction a minus sign.
- Conservation: total momentum before = total momentum after.
- If objects stick together, they move with one shared velocity.
- Force = change in momentum ÷ time.
Momentum questions
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Warm-up
Question 2Warm-upHigher
A 1200 kg car travels at 15 m/s. Calculate its momentum.
p = m × v.
Worked solution
- kg m/s
Answer: kg m/s
Exam-style
Question 3Exam-styleHigher
A 50 kg skater has a momentum of 500 kg m/s. How fast is she moving?
v = p ÷ m.
Worked solution
- m/s
Answer: m/s
Question 4Exam-styleHigher
A 2 kg trolley moving at 3 m/s hits a stationary 1 kg trolley. They stick together. Calculate their speed after the collision.
Momentum before = momentum after.
Worked solution
- Before: kg m/s
- After: , so m/s
Answer: m/s
Question 5Exam-styleHigher
A 1000 kg car at 20 m/s crashes into a stationary 1500 kg car and they move off together. Calculate their speed just after the crash.
Total mass after = 2500 kg.
Worked solution
- Before: kg m/s
- After: , so m/s
Answer: m/s
Question 6Exam-styleHigher
A 4 kg rifle fires a 0.02 kg bullet at 400 m/s. Both start at rest. Calculate the recoil speed of the rifle.
Total momentum before is zero, so after it must be zero too.
Worked solution
- Bullet: kg m/s forwards
- Rifle: , so m/s backwards
Answer: m/s (backwards)
Challenge
Question 7ChallengeHigher
A 0.15 kg ball is hit from rest to 30 m/s. The bat is in contact for 0.01 s. Calculate the average force on the ball.
F = change in momentum ÷ time.
Worked solution
- kg m/s
- N
Answer: N
Question 8ChallengeHigher
An airbag brings a 70 kg passenger from 10 m/s to rest in 0.5 s. Calculate the average force, and say why a longer stopping time is safer.
F = mΔv ÷ Δt.
Worked solution
- kg m/s
- N
- Spreading the same change of momentum over a longer time reduces the force.
Answer: N: a longer time makes the rate of change of momentum, and so the force, smaller
Common mistakes
- Ignoring directions (one object moving the other way).
- Forgetting to add the masses when objects stick together.
- Thinking a stationary object has momentum.
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Sources
The questions are our own. The “where it comes up” notes are from each board's published specification, checked on 27 October 2026:
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