# A moving trolley collides with a stationary trolley on a frictionless track. After the collision, the two trolleys stick together and move as one object. State the principle of conservation of momentum and use it to explain why the combined trolleys move more slowly than the original trolley was moving before the collision.

> Cambridge International IGCSE Physics (0625) — 1.6 Momentum · State and explain · 4 marks

## Mark scheme (4 marks)

1. The total momentum of a system remains constant / is conserved provided no external forces act
2. The stationary trolley had zero momentum before the collision, so total momentum before equals momentum of moving trolley alone
3. After the collision, the same total momentum is shared by / carried by a greater (combined) mass
4. Because momentum = mass × velocity, a greater mass with the same momentum must have a smaller velocity / moves more slowly

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](https://www.gradenine.co.uk/learn)
- [How to answer "State and 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-moving-trolley-collides-with-a-64d875f5) · Published by Druglandscape Ltd.