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Question
Calculate the work done by a car against gravity in moving along a straight horizontal road. The mass of the car is 400 kg and the distance moved is 2 m.
Solution
The weight of the car (mg) is vertically downward and the car is moving along the horizontal road, so the displacement of the car is in the long horizontal, i.e. angle between them is 90°.
Work done by weight of the car
W = Fs cos 90° = 0 .....(cos 90° = 0)
Hence, the work done by the car against gravity will also be zero.
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