JEE Advanced 2020 Concept Recapitulation Test 4 Paper 1

The vertical water tank, shown has uniform cross section, closed at the top and initial level of water in it is 4.5m from bottom. The empty space of length L contains air at atmospheric pressure (105Pa), that can be considered as an ideal gas. When the value at the bottom is opened, the level of water decreases by 0.5m when the flow of water ceases through valve remains opened. Neglecting any variation in temperature during the process, find initial length of empty space L in cm.(g=10m∕s2, density of water =1000kg∕m3)