# A sprinter starts from rest and accelerates along a straight track. After 4 seconds, the sprinter reaches a top speed of 10 m/s and then runs at this constant speed for a further 6 seconds before crossing the finish line. Describe the motion of the sprinter throughout the race and explain how the forces acting on the sprinter change between the two phases of the race.

> Edexcel A-Level Physics (9PH0) — 2.1 Motion · Describe and Explain · 5 marks

> A sprinter completes a 100 m race in two distinct phases: an acceleration phase lasting 4 seconds, followed by a constant speed phase lasting 6 seconds.

## Mark scheme (5 marks)

1. During the first phase, the sprinter accelerates (velocity increases from 0 to 10 m/s)
2. During the second phase, the sprinter moves at constant velocity / constant speed (10 m/s)
3. During the acceleration phase, the driving / forward force is greater than the resistive force (resultant force is not zero)
4. During the constant speed phase, the driving force equals the resistive force (resultant force is zero)
5. Links Newton's First Law — an object continues at constant velocity when the resultant force is zero, explaining why the sprinter maintains 10 m/s

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-sprinter-starts-from-rest-and-27b8c0fb) · Published by Druglandscape Ltd.