Question:
A porter lifts a heavy suitcase of mass $80 \mathrm{~kg}$ and at the destination lowers it down by a distance of $80 \mathrm{~cm}$ with a constant velocity. Calculate the workdone by the porter in lowering the suitcase.
$\left(\right.$ take $\left.\mathrm{g}=9.8 \mathrm{~ms}^{-2}\right)$
Correct Option: , 2
Solution:
$\mathrm{W}_{\text {Porter }}+\mathrm{W}_{\mathrm{mg}}=\Delta \mathrm{K} \cdot \mathrm{E} .=0$
$\mathrm{W}_{\text {Porter }}=-\mathrm{W}_{\mathrm{mg}}=-\mathrm{mgh}$
$=-80 \times 9.8 \times .8=-627.2 \mathrm{~J}$
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