# A car is travelling along a motorway at a constant speed. Explain why the car must have its engine running to maintain this constant speed.

> AQA GCSE Physics (8463) — 4.5.6 Forces and motion · Explain · 4 marks

> A car travels at a constant speed of 70 mph along a straight, level motorway.

## Mark scheme (4 marks)

1. There is a resistive / friction / air resistance force acting on the car (opposing motion)
2. The engine provides a driving force (forward / in the direction of motion)
3. The resultant force on the car is zero (driving force equals resistive force)
4. By Newton's First Law, a zero resultant force means the car continues at constant speed / velocity

## Key terms

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

## Related

- [Revision notes for AQA GCSE Physics (8463)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-car-is-travelling-along-a-07c9beaa) · Published by Druglandscape Ltd.