A cylindrical water tank of 50 cm diameter and 120 cm height is initially filled with water. The top of the tank is open to the atmosphere. A discharge plug is fitted at the bottom of the tank. When the plug near the bottom of the the tank is pulled out, a water jet streams out of the tank with a jet diameter of 1 cm. The mean velocity of the jet is given by $V=\sqrt{2gh}$ where h is the height of the water in the tank measured from the centre of the hole. Determine how long will it take for the water level in the tank to drop to 60 cm level from the bottom. Neglect the distance between the bottom of the tank ad the centre of the hole compared to the total water height.