Question

A boy of mass $50kg$, runs up a flight of $120$stairs, each measuring $25cm$ in one minute and forty seconds. If $g=10m{s}^{-2}$, the power of the boy is:

• A. $150W$
• B. $750W$
• C. $500W$
• D. $250W$

Answer 1

The correct option is A

$150W$

Step 1: Given data

Mass, $m=50kg$

No.of stairs$=120$

Length of stairs, $s=25cm=0.25m$

Time taken, $t=1min40s=100s$

Step 2: Calculating the power of the boy

$$\begin{gathered} Power\left(P\right)=Force\left(F\right)\times velocity\left(v\right) \\ \Rightarrow P=m\times g\times \frac{s}{t} \\ \Rightarrow P=50kg\times 10m{s}^{-2}\times \frac{0.25m}{100s} \\ \Rightarrow P=1.25W\times 120=150W \end{gathered}$$

Hence, the correct answer is option (A) i.e. $150W$