# A car is travelling along a straight, level road at a constant speed. The driver then presses the accelerator pedal and the car speeds up. Explain why the car travels at constant speed initially, and then describe what happens to the forces acting on the car when it accelerates.

> Eduqas GCSE Physics — 4.2 Forces, accelerations and Newton's laws of motion · Explain · 4 marks

## Mark scheme (4 marks)

1. At constant speed the driving force and resistive forces (friction/air resistance) are balanced / equal
2. Because the resultant force is zero, the car does not accelerate (Newton's First Law)
3. When the accelerator is pressed, the driving force increases / becomes greater than the resistive forces
4. There is now a resultant force in the direction of motion, causing the car to accelerate

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Physics](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-b4092261) · Published by Druglandscape Ltd.