A sprinter runs a 100 m race. During the first 4 seconds, the sprinter accelerates from rest to a top speed. For the next 6 seconds, the sprinter runs at this top speed. In the final 2 seconds, the sprinter decelerates and crosses the finish line at a lower speed. Describe the motion of the sprinter during each of the three stages of the race, referring to the sprinter's velocity and acceleration in each stage.

Edexcel GCSE Physics (1PH0) — 2.1 Motion · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A sprinter runs a 100 m race. During the first 4 seconds, the sprinter accelerates from rest to a top speed. For the next 6 seconds, the sprinter runs at this top speed. In the final 2 seconds, the sprinter decelerates and crosses the finish line at a lower speed.

Model answer (4 marks)

1. Acceleration phase – the sprinter’s speed rises from 0 to the top speed, so the velocity is increasing and the acceleration is positive.
2. Constant‑speed phase – the sprinter runs at the top speed, so the velocity is unchanged and the acceleration is zero.
3. Deceleration phase – the sprinter’s speed falls to a lower value, so the velocity is decreasing and the acceleration is negative (deceleration).

Examiner tips

  • Use the word ‘positive’ for accelerating, ‘zero’ for constant speed, ‘negative’ for decelerating.
  • Show the link between changing velocity and non‑zero acceleration.
  • Keep each stage short and clear.

Mark scheme (4 marks)

  1. During the first stage, the sprinter's velocity increases (from zero) so the acceleration is positive / greater than zero.
  2. During the second stage, the velocity is constant (at top speed) so the acceleration is zero.
  3. During the third stage, the velocity decreases so the acceleration is negative (deceleration).
  4. Correct use of the relationship that acceleration is the change in velocity divided by time (or equivalent), applied to distinguish the three stages — e.g. only when velocity is changing is there a non-zero acceleration.

Key terms in this question

velocity · acceleration

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