In loading a truck, a man lifts boxes of $100\ N$ each through a height of $1.5\ m$.
(a) How much work does he do in lifting one box?
(b) How much energy is transferred when one box is lifted?
(c) If the man lifts 4 boxes per minute, at what power is he working? $(g=10\ ms^{-2})$

(a). Here given, the weight of the box $mg=100\ N$

Height to be lifted $h=1.5\ m$

Therefore, work done to lift one box to the given height $W=mgh$

$=100\ N\times1.5\ m$   [Here take $mg=100\ N$]

$=150\ J$

Thus, $150\ J$ work is done to lift one box to the given height.

(B).  The energy transfer when one box is lifted will be equal to the work done to lift one box.

So, the energy transfer, when one box is lifted will be $150\ J$.

(C). Work done to lift 4 boxes $=4\times150\ J=600\ J$

Time taken to lift the 4 boxes $=1\ minute=60\ s$

Therefore, power $=\frac{work\ done}{time}$

$=\frac{600\ J}{60\ s}$

$=10\ W$

Thus, he is working with the power of $10\ W$.

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Updated on: 10-Oct-2022

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