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. How much work each does?
Take density of water = ${10}^{3}kg{m}^{-3}$ and $g=9.8Nk{g}^{-1}$

Answer 1

Work done by both the person will be the same because the weight of the water and the height is same.

We know that,

$1litre={10}^{-3}{m}^3$

$20litre=20\times {10}^{-3}{m}^3$

Mass of the water is,

$m=V\times \rho$

$=20\times {10}^{-3}\times 1000$

$=20kg$

The amount of work done is,

$W=mg\times h$

$=20\times 9.8\times 20$

$=3.92kJ$