Question

The radius of the base of a cone is $5$ cm and its height is $12$ cm. Its curved surface area is:

• A. $60\pi c{m}^2$
• B. $65\pi c{m}^2$
• C. $30\pi c{m}^2$
• D. $35\pi c{m}^2$

Answer 1

Answer: (B)

$65\pi c{m}^2$

The curved surface area of a cone $=\pi rl$, where $r$ is the radius and $l$ is slant height.

Given, $r=5cm$ and $h=12cm$.

We need to calculate slant height, using the formula $l^2=r^2+h^2$, where $h$ is height.

So, $l^{}=\sqrt{r^2+h^2}$ =$\sqrt{5^2+{12}^2}=13$.

We know,

curved surface area of a cone $=\pi rl$ $=\pi \times 5\times 13$ $=65\pi c{m}^2$

Hence, the answer is $65\pi c{m}^2$.

Therefore, option $B$ is correct.