Sol. The initial difference between the levels of water in the test-tube and the vessel can be found from the equation

P 0 = P – ρ gh,

Where P 0 is the external pressure, P is the pressure of air inside the test-tube and ρ is the density of the water. A freely falling body behaves as if it had no weight. Therefore, when it is falling freely, the column of water will not exert hydrostatic pressure and consequently the level of water in the test-tube will fall unit P = P 0 .