Problems on cones can be quite tricky so I would encourage you to look at this example. It also demonstrates decreasing functions.


  1. A cone of height 10cm and base radius 3cm is held vertex down and is filled with sand. A hole in the bottom of the cone allows the sand to escape at a steady rate of 0.5cm3 s-1. Find the rate that the depth is decreasing when the depth is 2cm.