A stone is thrown into a calm pond and circular ripples are formed at impact. If the radius expands at the rate of 0.5 feet/second, how fast is the circumference and the area of the ripples growing when the radius is 3 feet?

Answer 1

C = 2πr
dC/dt = 2π dr/dt

A = πr^2 dr/dt
dA = 2πr dr/dt

you have the values to plug in for both rates.