Question

Water is forced out of a fire extinguisher by air pressure, as shown in Figure. How much gauge air pressure in the tank (above atmospheric) is required for the water jet to have a speed of 30.0 m/s when the water level in the tank is 0.500 m below the nozzle?

Answer 1

The gauge air pressure in the tank:

$$p=\rho gh+0.5\rho v^2$$

$$p=1000( 9.8\cdot 0.5+0.5(30)^2)=455000\ Pa=455\ kPa$$