# A tennis ball travelling at 20 m/s strikes a stationary wall and bounces back in the opposite direction at 15 m/s. The contact time between the ball and the wall is very short. Explain, using Newton's laws of motion and the concept of momentum, what happens to the tennis ball during and after the collision, and why the wall does not appear to move.

> Edexcel A-Level Physics (9PH0) — 2.2 Forces, Newton's laws and momentum · Explain · 5 marks

> A tennis ball of mass 0.06 kg strikes a wall and bounces back. The ball is in contact with the wall for 0.005 s.

## Mark scheme (5 marks)

1. The ball experiences a change in momentum (impulse) because its velocity changes direction
2. A resultant force acts on the ball during contact (Newton's second law links force to rate of change of momentum)
3. By Newton's third law, the ball exerts an equal and opposite force on the wall
4. The total momentum of the ball-wall system is conserved (the change in momentum of the ball is equal and opposite to the change in momentum of the wall)
5. The wall does not appear to move because it is attached to a very large mass (the Earth/building), so its change in velocity is negligibly small

## Key terms

- [momentum](https://www.gradenine.co.uk/glossary/momentum)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-tennis-ball-travelling-at-20-3de42ab0) · Published by Druglandscape Ltd.