Question $2$: A $4m-$high, $3m-$diameter cylindrical water tank whose top is open to the atmosphere is initially filled with water. Now the discharge plug near the bottom of the tank is pulled out, and a water jet whose diameter is $50mm$ streams out. The average velocity of the jet is given by $V=\sqrt[\phantom{2}]{2}gh,$ where $h$ is the height of water in the tank measured from the center of the hole and $g$ is the gravitational acceleration. Determine how long it will take for the water level in the tank to drop to $2m$ from the bottom.