Question

A boy takes $3$ minutes to lift $20$ litres of water from a $20m$ deep well, while his father does the same in $2$ minutes. Compare :
(i) the work, and
(ii) power developed by them

Answer 1

As $1litre=1kg$ therefore, mass of $20litre$ water is $20kg$.

Both boy and his father does the same work.

Work done by each$=mgh=20\times 10\times 20=4000J$

The power is given as,

Power$=\frac{Work}{Time}$

Power of boy$=\frac{4000}{3\times 60}=22.22W$

Power of father$=\frac{4000}{2\times 60}=33.33W$

Thus power of father is one and half times that of boy.