1. The problem statement, all variables and given/known data A 3 cm radius rubber ball weighing 5 g is used to plug a 4cm hole in the base of a tank. The tank is in use and is gradually emptying. At approximately what depth will the plug fail by floating up and out of the hole? 2. Relevant equations Density 3. The attempt at a solution Ok so I don't have a numbers and all attempt at a solution :( But I do have a logical thought process as to how the solution should be solved, but I'm stumped on finding the volume of a partial sphere when given radius and the radius of the base circle - I know it is enough information I just cannot work out how to calculate it. The way I see it the upward force acting on the sphere will be proportional to the mass of the water displaced, whilst the downward force acting on the sphere will be proportional to the whole sphere so theoretically the plug should fail when the water level is at the height corresponding to the radius of the base circle on the opposite side. I am not sure about this though, as according to the figures given the density of the sphere is only 44 kg/m3 so all my common sense is telling me the plug wouldn't even work Am I taking the right approach?