# A car is travelling along a straight, level road at a constant speed. The driver then presses the accelerator pedal harder, causing the car to speed up. Explain why the car first travels at constant speed and then accelerates when the driver presses the accelerator harder.

> Edexcel GCSE Physics (1PH0) — 2.2 Forces and motion · Explain · 4 marks

> A car travels at constant speed along a level road. The driver then presses the accelerator pedal harder and the car speeds up.

## Mark scheme (4 marks)

1. At constant speed the driving force equals the resistive forces (friction/air resistance)
2. A resultant (net) force of zero means there is no change in motion / no acceleration
3. Pressing the accelerator increases the driving force so the driving force is now greater than the resistive forces
4. A resultant force in the direction of motion causes the car to accelerate (speed up)

## Key terms

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

## Related

- [Revision notes for Edexcel GCSE Physics (1PH0)](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-car-is-travelling-along-a-cd566bc8) · Published by Druglandscape Ltd.