Question

A stone dropped into a still pond sends out a circular ripple whose radius increases at a constant rate of 3 ft/sec. How rapidly is the area enclosed by the ripple increasing at the end of 10 sec?

Answer 1

\[A=\pi r^2\] and so \[A'=2\pi r r'\]

Answer 2

you are told \(r'=3\) therefore it is
\[A'=6\pi r\] and then you are asked to evaluate if \(r=10\) which should be easy now