Units (Forces and Motion)
3 marks · NormalA turning force (moment) of 7.5 newton metre (N m) is applied to a door to open it.
Name the physical quantity measured in newton metre, including its unit symbol.
A student gives the answer "joule (J)" for a question asking about moments. Explain why this is incorrect, based on SI units in Forces and Motion.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Moment (turning effect), unit: newton metre (N m) · must show moment, newton metre (N m)
(b) Joule (J) is the SI unit for energy, not for moment. The correct unit for the turning effect of force is newton metre (N m), as listed for Forces and Motion. · must show Joule is energy unit, not moment, newton metre is correct for moment
Common mistakes: confusing J with N m for moments
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Names 'moment' as the physical quantity, with correct unit (N m).
B2 (b) · 2 marks · Explains that joule (J) is for energy, not moment, which uses newton metre (N m).
Worked solution
a) The physical quantity is moment (turning effect of force), measured in newton metre (N m).
b) Joule (J) is the unit for energy. For moments (turning effect), the SI unit is newton metre (N m), not joule.