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Question
In Figure (i) the man walks 2 m carrying a mass of 15 kg on his hands. In Figure (ii), he walks the same distance pulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other end. In which case is the work done greater?
Solution
In Fig. (i), the force is applied horizontally, and the movement is also along the horizontal plane.
θ = 90°
W = Fs cos 90° = zero
In Fig. (ii), the force is applied in a horizontal direction, and the movement occurs horizontally as well.
Therefore, θ = 0°.
W = Fs cos θ = mg x s cos 0°
W = 15 x 9.8 x 2 x 1 = 294 joule.
Thus, work done in (ii) case is greater.
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