# A cyclist rides along a flat road at a constant speed. Explain why the cyclist must continue to pedal in order to maintain this constant speed, and describe what would happen to the motion of the cyclist if they stopped pedalling.

> Edexcel GCSE Physics (1PH0) — 9.1 Forces and their effects · Explain · 4 marks

> A cyclist is travelling along a flat, straight road at a steady speed. The cyclist notices that whenever they stop pedalling, they gradually slow down and eventually stop.

## Mark scheme (4 marks)

1. At constant speed, the thrust force from pedalling equals/balances the resistive forces (friction and/or air resistance/drag), giving a zero resultant force.
2. When the cyclist stops pedalling, the thrust force is removed/becomes zero.
3. There is now a resultant force acting on the cyclist in the direction opposite to motion (due to friction and/or air resistance).
4. This resultant force causes the cyclist to decelerate (slow down and eventually stop).

## 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-cyclist-rides-along-a-flat-e22e8662) · Published by Druglandscape Ltd.