Math Help - stone problem

1. stone problem

a stone dropped into a still pond sends out a circular ripple whose radius increases at a constant rate of 3 ft/s. how rapidly is the area enclosed by the ripple increasing at the end of 10s? ok im not sure how to set this up? would it be A = pi(r)^2 so i take the derivative with respect to r? right? i got 1960 pi as an answer..

2. Originally Posted by slapmaxwell1
a stone dropped into a still pond sends out a circular ripple whose radius increases at a constant rate of 3 ft/s. how rapidly is the area enclosed by the ripple increasing at the end of 10s? ok im not sure how to set this up? would it be A = pi(r)^2 so i take the derivative with respect to r? right? i got 1960 pi as an answer..
this is a related rates problem. you were given $\frac{dr}{dt} = 3$ ft/s
take the derivative of $A$ w/r to time, $t$ , and calculate the value of $\frac{dA}{dt}$ when r = 30 ft