A physics textbook lists the following four quantity–unit pairings. For each pairing, state whether the unit given is correct or incorrect, and for any incorrect pairing, give the correct SI unit.

Pearson Edexcel International GCSE Physics (4PH1) — 1.1 Units · State · 4 marks · View as Markdown

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

Quantity 1: momentum — unit given: kg/s Quantity 2: weight — unit given: N Quantity 3: acceleration — unit given: m/s² Quantity 4: moment of a force — unit given: kg m

Model answer (4 marks)

Momentum – kg/s is incorrect; correct unit is kg m/s
Weight – N is correct
Acceleration – m/s² is correct
Moment of a force – kg m is incorrect; correct unit is N m

Examiner tips

  • Use the exact wording from the mark scheme – e.g. "kg m/s" not "kg metres per second"
  • Show each quantity on a separate line for clarity
  • Include the word "incorrect" or "correct" as required

Common mistakes

  • Writing kg/s for momentum instead of kg m/s
  • Confusing weight with force and using N for both
  • Using kg m instead of N m for moment of a force

Mark scheme (4 marks)

  1. Momentum: kg/s is incorrect; correct unit is kg m/s (kilogram metres per second)
  2. Weight: N (newton) is correct
  3. Acceleration: m/s² is correct
  4. Moment of a force: kg m is incorrect; correct unit is N m (newton metre)

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