Question

A boy weighing $350N$ runs up a flight of $30$ steps each $20cm$ high in $1$ minute, Calculate power spent:

• A. $350W$
• B. $3.5W$
• C. $35W$
• D. $3500W$

Answer 1

Answer: (C)

$35W$

As there are $30$ steps with $20$ cm each.
Total distance would be, $s=30\times 20cm=600cm$, which is in general $6m$.
Given
$Force,F=350N$
$Time,t=1min=60s$
$Work,W=F\times s\times \cos \theta$
$W=350\times 6\times \left(cos180\right)=-2100W$
Hence, a work of $2100N$ is done against gravity.
$Power,P=\frac{W}{t}=\frac{2100}{60}J/s=35W$

So, the correct option is $\left(C\right)$