# Related rates problem

• Oct 3rd 2009, 02:21 PM
nautica17
Related rates problem
Well here is the problem I'm given.

"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 10 s?"

So where do I start? Would I just use the equation for the area of a circle? I tried that and I don't quite know where to plug in the 10 sec.
• Oct 3rd 2009, 02:42 PM
skeeter
Quote:

Originally Posted by nautica17
Well here is the problem I'm given.

"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 10 s?"

So where do I start? Would I just use the equation for the area of a circle? I tried that and I don't quite know where to plug in the 10 sec.

take the derivative w/r to time of the circle area equation ... then substitute in your given information to find $\displaystyle \frac{dA}{dt}$