Question

The curved surface area of a hemisphere is $77c{m}^2$. The radius of the hemisphere is :

• A. $3.5cm$
• B. $7cm$
• C. $10.5cm$
• D. $11cm$

Answer 1

The correct option is A $3.5cm$

Le the radius of hemisphere be ${}^{\prime }r$ cm.

Now, cuoved surface area of hemisphere $=2\pi r^2$

$\Rightarrow 2\pi r^2=77$

$\Rightarrow r^2=\frac{77\times 7}{2\times 22}=\frac{7\times 7}{2\times 2}$

$\Rightarrow r=\sqrt{\frac{49}{21}}=\frac{7}{2}$

$\Rightarrow r=3.5cm$