Question

A circular disc of radius $3$ cm is being heated. Due to expansion, its radius increases at the rate of $0.05cm/s$. Find the rate at which its area is increasing when radius is $3.2$ cms.

Answer 1

As we know,

Area of circular disc $A=\pi r^2$

$dA=2\pi rdr$

On substituting following values in above expression,

$r=3.2cm,dr=0.05cm/s$

We get

$dA=1.0053c{m}^2/s$