A cylindrical can of height h and radius r is to be made with a fixed volume V. Show that the area of material used is minimised when h = 2r.

A tank, shaped like a cone has height 4 meter and base radius 5 meter. It is placed so that the circular part is upward. It is full of water, and we have to pump it all out by a pipe that is always leveled at the surface of the water. Assume that a cubic meter of water weighs 10000N, i.e. the density of water is 10000- How much work does it require to pump all water out of the tank? Enter the exact value of your answer. N m³ W Joules