Question

How many cubic metres of earth must be dugout to sink a well 21 m deep and 6 m diameter? Find the cost of plastering the inner surface of the well at Rs. 9.50 per $m^2$.

Answer 1

Diameter of a well = 6 m

$\therefore$ Radius (r) $=\frac{6}{2}=3$ m Depth (h) = 21 m

$\therefore$ Volume of earth dugout = $\pi r^{2}h$

=$\frac{22}{7}\times 3\times 3\times 21m^3=594m^3$

and curved surface area = 2$\pi$ r h =$2\times \frac{22}{7}\times 3\times 21=396m^2$

Rate of plastering the surface = Rs. 9.50 per $m^2$

$\therefore$ Total cost = Rs. 9.50 $\times$ 396 = Rs. 3762