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Four persons jointly lift a 250 kg box to a height of 1 m and hold it. 

(a) Calculate the work done by the persons in lifting the box. 

(b) How much work is done for just holding the box? 

(c) Why do they get tired while holding it? (g = 10 m/s2). 

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1 Answer

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(a) Given, 

Force, F = 250 × 10 = 2500 N 

Displacement, s = 1 m 

Work done = F × s = 2500 × 1 = 2500 J 

(b) As there is no displacement in just holding the box, so no work is done i.e. Work done is zero. 

(c) To hold the box men are applying force against the gravity, which involves their muscles to work, hence they get tired holding it.

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