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? $(g=10\ ms^{-2})$

AcademicPhysicsNCERTClass 9

Mass of the box, $m=250\ kg$

Height $h=1\ m$

$(a)$. Work done by the men in lifting the box $=mgh=250\times 10\times 1$

$=2500\ J$

$(b)$. When the men just hold the box, then there is no displacement, so no work is done.

$(c)$. In order to hold the box at a certain height, men are applying a force that is equal and opposite to the gravitational force acting on the box. While applying the force, muscular effort is involved.
So, men get tired while holding it.
Updated on 10-Oct-2022 13:28:52