Question

The curved surface area of a right circular cone of height $84cm$ and diameter $70cm$ is:

• A. $10010$ $c{m}^2$
• B. $100000$ $c{m}^2$
• C. $10020$ $c{m}^2$
• D. $11000$ $c{m}^2$

Answer 1

Answer: (A)

Given, $h=84cm$ is the height of right circular cone and diameter is $d=70cm$.

Then radius of right circular cone $=\frac{d}{2}=\frac{70}{2}=35cm$.

Therefore, the curved surface area of a right circular cone

$=\pi rl$

$=\pi r\left(\sqrt{r^2+h^2}\right)$

$=\frac{22}{7}\times 35\left(\sqrt{(84{)}^2+(35{)}^2}\right)$

$=110\left(\sqrt{7056+1225}\right)$

$=110\times 91=10010$ $c{m}^2$.

Hence, option $A$ is correct.