A boy of mass $40\ kg$ runs up flight of $50$ steps each $10\ cm$ high in $5$ seconds. Find: (i) the work done by the boy. (ii) the power developed. $( g=9.8\ ms^{-2})$.

Here given mass $m=40\ kg$

Number of steps $=50$

Height of each step $=10\ cm=\frac{10}{100}\ m=\frac{1}{10}\ m$

Total height climbed $=$ Number of steps$\times$ Height of each step

$=50\times\frac{1}{10}$

$=50\ m$

Time taken by the boy to climb $t=5\ sec.$

Acceleration $g=10\ ms^{-2}$

Therefore $( i)$. Work done by the boy $W=mgh$

Or $W=40\times10\times\frac{1}{10}$

Or $W=40\ Joule$ 

$( ii)$. Power developed$=\frac{Work\ done}{time}$

$=\frac{40}{5}$

$=8\ Watt$

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Updated on: 10-Oct-2022

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