Question

A boy of mass $40kg$ runs up a flight of $50$ steps, each $10cm$ high in $14s$. So, work done by the boy is:

• A. $1960J$
• B. $19.6J$
• C. $980J$
• D. $9.8J$

Answer 1

The correct option is A $1960J$

Mass of the boy, $m=40kg$

Number of steps = $50$

Height of each step = $10cm$

Force on the boy due to gravity, $F=mg=40\times 9.8N=392N$
While climbing up the steps, the boy does work against gravity.
Displacement in the vertical direction, $s=(50\times 10)cm=500cm=5m$

Displacement is in the direction of force applied by the boy against gravity.
So, work done, $W=F\times s=392\times 5J=1960J$