An artificial satellite is moved from a low orbit to a higher orbit around the Earth, whilst its orbital period remains the same. State and explain what happens to the orbital speed of the satellite.

Pearson Edexcel International GCSE Physics (4PH1) — 8.1 Motion in the universe · Explain · 4 marks · View as Markdown

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

An artificial satellite orbits the Earth. Engineers decide to increase its orbital radius whilst keeping its orbital period unchanged.

Model answer (4 marks)

The orbital speed increases.

For a fixed orbital period the speed is proportional to the orbital radius.

A larger radius means a larger circumference, so the satellite must travel a greater distance in the same time.

Hence a greater speed is required to complete one orbit in the unchanged period.

Examiner tips

  • Use the command word ‘explain’ – give a short reason for each point.
  • Show the proportionality (speed ∝ radius) and link it to the distance travelled.
  • Keep the answer concise – 4–5 short sentences is enough for full marks.

Common mistakes

  • Saying the speed decreases – the relationship is opposite.
  • Failing to mention the larger circumference or the need to cover more distance.
  • Using vague wording like ‘it will change’ without explaining why.

Mark scheme (4 marks)

  1. The orbital speed increases
  2. Orbital speed is proportional to orbital radius (for a fixed period)
  3. The satellite must cover a greater distance (larger circumference) in the same time
  4. Therefore a greater speed is needed to complete one full orbit in the same orbital period

Key terms in this question

orbital speed · orbital period · artificial satellite

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