Question

A boy of mass $40kg$ runs up a flight of $15$ steps each $15cm$ high in $10s$. Find the work done? Take $g=10N$ $k{g}^{-1}$

• A. $9J$
• B. $90J$
• C. $900kJ$
• D. $900J$

Answer 1

The correct option is D $900J$

$Force=m\times g=40\times 10=400N$
$Workdone=F\times S\times \cos \theta$
Here we have 15 steps with 15 cm each hence total displacement is 225 cm that is 2.25 m
$W=400\times 2.25=900J$
Hence we need to apply an energy of $900J$.