Determining diameter of a ball floating in a freshwater pond.
A child at a park finds a ball floating in a freshwater pond (temperature 30°C). The child swims to the ball and, with an incredible amount of dexterity, balances himself on the ball. When he does so, ball sinks to the point where none of it extends out of the water and remains submerged such that child does not sink. The child has a mass of 36kg. What is the diameter of the ball? Presume for this problem that the ball has negligible mass (including the air inside it).