Question

If the radius of the base and the height of a right circular cone are respectively $21$ cm and $28$ cm, then the curved surface area of the cone is $(\pi =\frac{22}{7})$:

• A. $3696c{m}^2$
• B. $2310c{m}^2$
• C. $2550c{m}^2$
• D. $2410c{m}^2$

Answer 1

The correct option is B $2310c{m}^2$

For a cone, slant height $l=\sqrt{h^2+r^2}$; where $h$ is the height.

Hence, $l=\sqrt{{28}^2+{21}^2}$

$l=35$ cm.

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

Hence, curved surface area of this cone $=\frac{22}{7}\times 21\times 35=2310{cm}^2$.

Therefore, option $B$ is correct.