Question

A right circular cylinder has a volume of $81\pi$. If the circumference of the base is $6\pi$, what is the height?

• A. 6
• B. 9
• C. 12
• D. 15

Answer 1

Answer: (B)

9

Volume of the right circular cylinder $V=\pi r^{2}h$

Here $V=81\pi$ and $c=6\pi$

Circumference $=$ $2\pi r$

$\Rightarrow 6\pi =2\pi r$

$\Rightarrow r=\frac{6\pi }{2\pi }=3$

$\therefore 81\pi =\pi (3{)}^{2}h$

$\Rightarrow h=\frac{81\pi }{9\pi }=9$