The solution is:
where is the initial volume and is the initial velocity. I can't be bothered going through all the working as it would take too long to Late !
Find the time required for an inverted conical tank of radius and height to empty through a round hole of cross sectional area at the bottom. Given that the water flows according to the formula where and are respectively the velocity of flow through the hole and the height of water level above the hole at time and is the acceleration due to gravity.