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  • four men lift a 250 kg box to a height of 1 m 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 = 10 ms^-2)

Four men lift a 250 kg box to a height of 1 m 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 = 10 ms^{-2})

Answers (1)

Solution.

Mass of the box = 250 kg
Height attained = 1 m
(a) Work done in lifting the block will be stored as potential energy
W=PE=mgh
After calculating, the work done will be 2500 joule. 
(b) When they hold it in the air without any movement, the displacement of box will be zero.
We know work is defined as:
W=Fd\cos \theta
Hence, work done will be zero.
(c) When they hold it in air without any movement, their muscles are stretched.
These stretched muscles requires energy and causes fatigue and tiredness.

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