Time of emptying a hemispherical tank through an orifice at its bottom
Key FactsGyroscopic Couple: The rate of change of angular momentum () = (In the limit).
- = Moment of Inertia.
- = Angular velocity
- = Angular velocity of precession.
Blaise Pascal (1623-1662) was a French mathematician, physicist, inventor, writer and Catholic philosopher.
Leonhard Euler (1707-1783) was a pioneering Swiss mathematician and physicist.
OverviewConsider a hemispherical tank, containing some liquid and having an orifice at its bottom as shown in figure. Let,
- = Radius of the tank
- = Initial height of the liquid
- = Final height of the liquid
- a = Area of the orifice
At some instant, let the height of the liquid be h above the orifice.We know that the theoretical velocity of the liquid at this instant, At this instant, let r be the radius of the liquid surface. Then the surface area of the liquid, After a small interval of time dt, let the liquid level fall down by the amount dh. Therefore volume of the liquid that has passed in time dt,
The value of dh is taken as negative, as its value will decrease with the increase in discharge.We know that the volume of liquid that has passed through the orifice in time dt, = Coefficient of discharge Area Theoretical velocity Time 2) and (3)
Substituting this value of in equation (4)
5) between the limits to i.e.,
If the vessel is to be completely emptied, then putting in this equation,
If the vessel was full at the time of the commencement and is to be completely emptied, then putting in the above equation,
Example - Time of emptying a hemispherical tank
A hemispherical tank of 2 meters radius contains water up to a depth 1meter. Find the time taken to discharge the tank completely through an orifice of 1000 mm2 provided at the bottom. Take = 0.62.
- = 2m
- = 1m
- = 1000 mm2
- = 0.62
Time taken to discharge the tank completely = 43 min 13 sec