Question

If the circumference at the base of a right circular cone and the slant height are $120\pi$ $cm$ and $10cm$ respectively, then the curved surface area of the cone is equal to:

• A. $1200\pi$ ${cm}^2$
• B. $600\pi$ ${cm}^2$
• C. $300\pi$ ${cm}^2$
• D. $600$ ${cm}^2$

Answer 1

The correct option is B $600\pi$ ${cm}^2$

Given,

circumference $=120\pi cm$ and slant height$\left(l\right)=10cm$

$\Rightarrow 2\pi r=120\pi$

$\Rightarrow 2r=120$

$\Rightarrow r=60cm$.

We know, the curved surface area of the cone $=\pi rl$.

$=\pi \times 60\times 10$

$=600\pi c{m}^2$

Hence, option $B$ is correct.