In ancient egypt, circular vessels filled with water sometimes were used as crude clocks. the vessels were shaped in such a way that, as water drained from the bottom, the surface level dropped at constant rate, s. assume that water drains from a small hole of area a. find an expression for the radius of the vessel, r, as a function of the water level, h. obtain an expression for the volume of water needed so that the clock will operate for n hours.