Question

A hose directs a horizontal jet of water, moving with a velocity of 20m/s, on to a vertical wall. The cross-sectional area of the jet is 5 x 10-4m2. If the density of water is 1000kg/m^3, calculate the force on the wall assuming the water is brought to rest there.

Answer 1

Since Force is defined as the rate of change of the linear momentum.

Volume of water coming out of the pipe per sec, $= A×v=20×10^{−4}×5=0.01m^3/s$

Then, mass of water hitting the wall per sec $m = 0.01×10^3 =10 kg/sec$

Force, $F =\frac{2mv}{t} ​=2×10×20=400N$