Answer:
(a) Consider a coolie carrying a load on his head across
a level road. He exerts an upward force which is equal to the weight of the
load. But the displacement of the load is in the horizontal direction. The
angle between force ?F and displacements s is 90°.
Hence, W = Fs cos 90° = 0
(b) Here, h = 20 m, m = 2000 kg,
t = 15 min =15 x 60 = 900
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