Here is a related rates y'all may like to tackle.

"a circular tank with height 2 feet, radius on the top of R and radius on the bottom of r where R>r.

If R=6 ft and r=4.5ft, and it's filling at a rate of 15 ft^3/min, how fast is the height of the water changing when the water's radius is 5?


Of course, this forms a frustum of a cone. But, there is a trick that makes this quite easy to find dh/dt.