Imagine this, a cylindrical tank with a liquid level height ‘h’. The tank develops a leak in the bottom; Torricelli’s Law says that “Water in an open tank will flow out through a small hole in the bottom with the velocity it would acquire in falling freely from the water level, h.”

If a mass of water ‘m’ fell freely from height ‘h’, the GPE of the mass would be transformed into KE.

mgh=12mv2[IMG]file:///C:\DOCUME~1\Operator\LOCALS~1\Temp\msohtmlclip1\01 \clip_image002.gif[/IMG]

2gh=v2[IMG]file:///C:\DOCUME~1\Operator\LOCALS~1\Temp\msohtmlclip1\01 \clip_image004.gif[/IMG]

Therefore according to Torricelli’s Law, the velocity that the water exits the tank isv=2gh, where g = 9.8m/s^{2}.

The change in volume of the tankdVdt=(Venterings)/s-(V(leaving))/s

- Find a relationship for the amount of water leaving the tank per unit time (
dVdt[IMG]file:///C:\DOCUME~1\Operator\LOCALS~1\Temp\msohtmlclip1\01 \clip_image002.gif[/IMG], m^{3}per second) using the area of the hole and the velocity of the water. (Volume entering is 0 L/s)

- Use the chain rule
dVdt=dhdt×dVdhto develop the differential equationdhdt=f(h). Solve the equation to find the relationshiph(t)[IMG]file:///C:\DOCUME~1\Operator\LOCALS~1\Temp\msohtmlclip1\01 \clip_image008.gif[/IMG].

A full water tank is 1.8m high and has a radius of 2m, a small hole of area 5cm^{2}is created in the bottom of the tank, how long does it take for the tank to empty.

- Consider a tank of the same dimensions as above. The tank is half full when the hole develops and water now enters the tank at a rate of 10L/s. How long does it take to fill/empty the tank?

[IMG]file:///C:\DOCUME~1\Operator\LOCALS~1\Temp\msohtmlclip1\01 \clip_image008.gif[/IMG]