A swimmer dives off a starting block and swims along a straight lane. For the first part of the swim the swimmer moves at a constant velocity. She then decelerates uniformly until she reaches the end of the pool and stops. Describe what a velocity-time graph of the swimmer's entire journey would look like, and explain what the area under the graph represents.

Pearson Edexcel International GCSE Physics (4PH1) — 1.2 Movement and position · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

The graph consists of two parts. The first part is a horizontal straight line, showing that the swimmer’s velocity is constant. The second part is a straight line that slopes downward to the time axis, showing a negative gradient and therefore uniform deceleration until the velocity reaches zero at the end of the pool. The area under the whole graph is the total distance travelled by the swimmer.

Examiner tips

  • Use a horizontal line for constant velocity, a straight downward line for uniform deceleration, and end the graph at zero velocity.
  • Show that the area under the curve equals distance – mention displacement if the swimmer moves in one direction.

Common mistakes

  • Drawing a curved or jagged deceleration line instead of a straight one.
  • Failing to end the graph at zero velocity or not recognising the area as distance travelled.

Mark scheme (4 marks)

  1. The first section of the graph is a horizontal straight line (showing constant velocity).
  2. The second section of the graph is a straight line with a negative gradient (sloping downward to zero) showing uniform deceleration.
  3. The line ends at zero (velocity = 0) showing the swimmer has stopped.
  4. The area under the velocity-time graph represents the total distance travelled by the swimmer.

Key terms in this question

velocity-time graph · constant velocity

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