Question

The radius of a conical vessel is $21$ cm and the vertical height is $20$ cm. What is the length of the cloth used to cover its surface, if the width of the cloth is $50$ cm?

Answer 1

$l=\sqrt{r^2+h^2}=\sqrt{{21}^2+{20}^2}$
$=\sqrt{841}=29cm$
$\therefore$ Curved surface of the vessel
= Area of the cloth used
$=\pi rl$
$=\frac{22}{7}\times 21\times 29c{m}^2$
$=1914c{m}^2$
$\therefore$ length of the cloth $=\frac{1914}{50}cm$
$=38.28cm$