Energy and work
2 marks · EasyAn athlete holds a heavy backpack still above their head for 10 seconds. Explain why no work is done on the backpack, even though the athlete is exerting a force upward.
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No work is done on the backpack because it does not move. Work is only done when a force causes movement in the direction of the force.
Also accept: There is no distance moved in the direction of the force, so work done is zero.
Common mistakes: Thinking time or effort alone means work is done.; Forgetting that movement is required for work.
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Marking points
B1 · 1 mark · States the backpack does not move.
B2 · 1 mark · Explains that work is only done if there is movement in the direction of the force.
Worked solution
No work is done on the backpack because it does not move. Work requires both a force and movement in the direction of the force. Since the distance moved is zero, the work done is also zero.