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

> Edexcel A-Level Physics (9PH0) — 9.1 Kinetic theory and ideal gases · Explain · 5 marks

> A cyclist is travelling along a flat, straight road at a constant velocity of 12 m/s. The cyclist continues to pedal to maintain this speed.

## Mark scheme (5 marks)

1. At constant velocity, the resultant force is zero (forces are balanced)
2. Friction and/or air resistance act on the cyclist in the opposite direction to motion
3. The pedalling provides a thrust / driving force to balance (equal) these resistive forces
4. If the cyclist stops pedalling, the thrust is removed so the resultant force is no longer zero / a resultant force now acts in the direction of friction/air resistance
5. The cyclist decelerates (slows down) because the resultant force opposes motion

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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-142b341b) · Published by Druglandscape Ltd.