. A rock drops into a still lake, creating a circular ripple that expands so that the radius grows at a rate of

Question

. A rock drops into a still lake, creating a circular ripple that expands so that the radius grows at a rate of 
1.5 feet per second. At the moment when the area is 16π square feet, find the rate of change of the 
following: a) the area and b) the circumference

oobleck · Accepted Answer

when A = 16π, r=4, C = 2πr = 8π dA = C dr, so (a) dA/dt = 8π * 1.5 = 12π ft^2/s (b) dC/dt = 2π dr/dt = 3π ft/s

Money$$$$$$$ · Answer

Thanks oobleck