# A lorry and a small car are both travelling at the same speed when their drivers each notice a hazard at the same moment. Both drivers are fully alert and have identical reaction times. Explain why the lorry has a greater stopping distance than the small car.

> Eduqas A-Level Physics — 4.2 Kinetic theory and gases (A-Level only) · Explain · 5 marks

> The lorry has a much greater mass than the small car. Both vehicles are travelling at the same speed and both drivers react at the same time. The road and weather conditions are identical for both vehicles.

## Mark scheme (5 marks)

1. The thinking distance is the same for both vehicles
2. The lorry has a greater momentum than the small car (at the same speed)
3. A greater change in momentum is needed to stop the lorry
4. The braking force available cannot fully compensate, so the braking distance is greater
5. Therefore the total stopping distance (thinking distance + braking distance) is greater for the lorry

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Physics](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-lorry-and-a-small-car-0e5f9b58) · Published by Druglandscape Ltd.