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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?
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Solution
In figure (i), force is applied on the mass, by the man in vertically upward direction but distance is moved along the horizontal.
∴ θ = 90°
W = F s cos 90° = zero
In figure (ii), force is applied along the vertical and the distance moved is also along the vertical.
∴ θ = 0°.
W = F s cos θ = mg × s cos 0°
W = 15 × 9.8 × 2 × 1 = 294 joule.
Thus, work done in case (ii) is greater.
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