AP Physics Questions

1. The drain on a bath tub is 0.50 m below the level of the water when the plug is removed. At approximately what speed will the water emerge from the tub? Don’t worry about the shape of the orifice.

2. Water is flowing into a below – deck compartment of a ship through a hole in its side at a speed of 10.0 m/s. How far beneath the water’s surface is the hole?

The answer to this problem is 5.10 m.


The Bernoulli principle states that the sum of the static pressure $\rho g h$ and the dynamic pressure $\rho*v^2/2$ is the same in each point of a current tube of an ideal fluid. Considering water ideal one can write

$\rho g h = \rho*v^2/2$ where h is the height of the water column and v is the speed at drain output.

($\rho$ is the water density)

$v = \sqrt{(2 g h)} = \sqrt{2*9.81*0.5} = 3.13 m/s$

2. One can apply the same principle.

$\rho g h = \rho*v^2/2$

$h = v^2/2/g = 10*10/2/9.81 =5.10 m$