Four men light a 250 kg box to a height of 1m and hold it without raising or lowering it. (a) How much work is done by the men in lifting the box ? (b) How much work do they do in just holding it ? (c ) why do they get tired while holding it ? `(g = 10m//s^2)`

Explanation

Given, m = 250 kg, height (h) =1m and acceleration due to gravity `g=10ms^(-1)`
(a) Work done by the man in lifting the box
W= Potential energy of box
W = mgh
`W=250xx1xx10=2500J`
(b) Work done is zero in holding a box, because displacement is zero.
In holding the box, the energy of man loses. Due to loss of energy he felt tired.