Question

A stream of water flowing horizontally with a speed of $15m{s}^{-1}$ gushes out of a tube of cross-sectional area ${10}^{-2}{m}^2$, and hits a vertical wall nearby. What is the force exerted on the wall by the impact of water, assuming it does not rebound?

Answer 1

Speed of the water stream, v = 15 m/s
Cross-sectional area of the tube, $A={10}^{-2}{m}^2$
Volume of water coming out from the pipe per second,
$V=AV=15\times {10}^{-2}{m}^3/s$
Density of water, $\rho ={10}^{3}kg/m^3$
Mass of water flowing out through the pipe per second $=\rho \times V=150kg/s$
The water strikes the wall and does not rebound. Therefore, the force exerted by the water on the wall is given by Newton's second law of motion as:
F = Rate of change of momentum = $\frac{\Delta p}{\Delta t}$ = $\frac{mv}{t}=150\times 15=2250N$