# A car is travelling along a straight, level road at a constant velocity. The driver then presses the accelerator pedal and the car accelerates. Explain, using Newton's laws of motion, why the car travels at constant velocity before the driver presses the accelerator, and why the car accelerates after the driver presses the accelerator.

> Eduqas A-Level Physics — 1.2 Forces and Newton's laws · Explain · 5 marks

## Mark scheme (5 marks)

1. At constant velocity, the driving force equals the resistive forces (e.g. friction/air resistance)
2. A resultant force of zero means there is no change in motion (Newton's First Law)
3. When the accelerator is pressed, the driving force increases
4. The driving force is now greater than the resistive forces, so there is a resultant force in the direction of motion
5. A resultant force causes acceleration in the direction of that force (Newton's Second Law)

## Key terms

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

## 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)
- [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-c5cf98e2) · Published by Druglandscape Ltd.