THE TURNING EFFECT OF FORCES
4 marks · NormalA mechanic uses a wrench to loosen a bolt. The wrench is 0.30 m long, and he applies a force of 150 N perpendicular to the wrench at its end.
Calculate the moment produced by the mechanic about the centre of the bolt.
Explain what would happen to the moment if the mechanic applied the same force closer to the centre of the bolt.
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) 45 Nm · must show moment = 150 N × 0.30 m, 45 Nm
(b) The moment would be smaller because the distance from the centre of the bolt is reduced. Moment is directly proportional to distance from the pivot. · must show moment decreases, moment depends on distance
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Marking points
M1 (a) · 1 mark · Correctly uses moment formula (moment = force × perpendicular distance)
A1 (a) · 1 mark · Evaluates moment as 45 Nm with correct units
B1 (b) · 1 mark · States that the moment would be smaller/less
B2 (b) · 1 mark · Explains that moment depends on the distance from the pivot (direct proportionality)
Worked solution
a) Moment = force × perpendicular distance
b) The moment would be smaller because the distance from the pivot is reduced. Moment is directly proportional to the perpendicular distance from the pivot (M = F × d).