Rate of Change in Water Depth of Cone-Shaped Tank

[ProblemSets]

The base of a cone-shaped tank is a circle of radius 5 feet, and the vertex of the cone is 12 below the base. The tank is filled to a depth of 7 feet, and water is flowing out of the tank at a rate of 3 cubic feet per minute.

Find the rate of change of the depth of the water in the tank.

 

[Feldoh]

I find it helpful to think about what it is exactly I'm asked to find. Do you know what your are looking for?