A geometry/derivative word problem

Quote:

a container has the shape of an open right circular cone, as shown in the figure above. The height of the container is 10 cm and the diameter of the opening is 10 cm. Water in the container is evaporating so that it depth h is changing at the constant rate of -3/10 cm/hr.

The volume of a cone of height h and radius r is given by V=1/3 pi r^2 h

a) Find the volume V of water in the container when h=5 cm.

b) find the rate of change of volume of water in the container, with respect to time, when h=5 cm.

I know you suppose to find an equation and take the derivative, but how to do it i don't know.

Re: A geometry/derivative word problem

The diameter is 10. The radius is 5 cm.

Re: A geometry/derivative word problem

think he probably either graduated or failed out by now....

Re: A geometry/derivative word problem

Sure, but other people may look at the answer.