A newton-meter is used to measure the weight of a gold coin on Earth. The same coin is then taken to the surface of a planet where the gravitational field strength is greater than on Earth. State what happens to the weight of the coin and to the mass of the coin on this planet, and explain why each changes or stays the same.

Cambridge International IGCSE Physics (0625) — 1.3 Mass and weight · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

The weight of the coin increases on the planet
Because weight depends on gravitational field strength (W = mg), and g is greater on this planet
The mass of the coin stays the same
Because mass is the amount of matter in the coin and does not depend on gravitational field strength / location

Examiner tips

  • Use the formula W = mg to link weight to g
  • State clearly that mass is invariant under change of location
  • Show the reasoning for each part separately

Common mistakes

  • Confusing weight with mass
  • Writing that mass increases because of stronger gravity
  • Using the wrong unit (kg instead of N) for weight

Mark scheme (4 marks)

  1. The weight of the coin increases on the planet
  2. Because weight depends on gravitational field strength (W = mg), and g is greater on this planet
  3. The mass of the coin stays the same
  4. Because mass is the amount of matter in the coin and does not depend on gravitational field strength / location

Key terms in this question

weight · mass · gravitational field strength

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