Four persons jointly lift a 250 kg box to a height of lm and hold it. (a) Calculate the work done by the persons in lifting the box. (b) How much work do they do just holding it ? (c) Why do they get tired while holding it ? (g = 10 m s^2)

(a) Here, F = mg = 250 x 10 N,
S = 1 m
Work done is given by W = F x S .
= 2500 N x 1 m = 2500 J

(b) No work is done in just holding the weight because there is no displacement
i.e., S = 0, W = FS = 0.

© They get tired because of muscular effort that they have to apply in supporting the weight.