Give one situation where force is applied but no work is done

CBSE Class 9 CBSE Class 9 Science
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1

(i) Give one situation where force is applied but no work is done. Explain, why?
(ii) A pump is used to raise water to a height of 20 m. It transfers 2000 kg of water in 15 min. Calculate power of the pump. (Take, g = 10 m)

2

(i) Consider a coolie carrying a load on his head across a levelled 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 Fand displacement s is 90°.
Hence, W = Fs cos 90° = 0
(ii)Here, h =20m
m = 2000kg
t = 15 min = 15 x 60 = 900 s
Power P = mgh / t = 2000 x 10 x 20 / 900 = 444.44 ${{Js}^{-1}}$