A cylindrial tank being drained through a duct whose cross-sectional area is 3x10-4 m2. The velocity of the water at the exit varies according to (2gz)0.5, where z is the water level, in m, and g is the acceleration of gravity, 9.81 m/s2. The tank initially contains 2500 kg of liquid water. Taking the density of the water as 1000 kg/m3, determine the time, in minutes, when the tank contains 900 kg of water.