Question

The height of a right circular cylinder is $10.5cm$. If three times the sum of the area of its two circular faces is twice the area of the curved surface area. Find the radius of its base.

Answer 1

ht. of a cylinder $=10.5cm$

Let ${}^{\prime }{r}^{\prime }$ be the radius of cylinder

Also, Area of $2$ bases of cylinder $=2\left(\pi r^2\right)$

C.S. Area of cylinder $=2\pi rh$

Acc. to question,

$3\left(2\pi r^2\right)=2\left(2\pi rh\right)$

$\Rightarrow 36\pi r^2=4\pi rh$

$\Rightarrow 3r=2h$

$\Rightarrow 3r=2\times 10.5=21$

$r=\frac{21}{3}=7$

$\therefore$ radius of cylinder $=7cm$