Question

Calculate the work done in raising a stone of mass $5kg$ and specific gravity $3$, lying at the bed of a lake through a height of $5m$.

Answer 1

Loss of weight in water $=\frac{\text{Weight in air}}{\text{Specific gravity}}$

$=\frac{5}{3}$

Weight of stone in water $=5-\frac{5}{3}$

$=\frac{10}{3}$

Force $=\frac{10}{3}\times 9.8$

$=\frac{98}{3}$

Work done $=4\times \frac{98}{3}$

$=130.7J$