Physics - Fluid Question with Solution | TestHub

Volume of water coming out of the pipe per sec $=Av=10\times {10}^{-4}\times 20=0.02 {\mathrm{m}}^3 {\mathrm{s}}^{-1}$

Mass of water hitting the wall per second $m=0.02\times {10}^3=20 \mathrm{kg} {\mathrm{s}}^{-1}$

As the water hits the wall normal to the wall and stops, the change of momentum of water hitting the wall is $=m\left(0-\left(-v\right)\right)=mv$

$=20\times 20=400 \mathrm{kg} \mathrm{m} {\mathrm{s}}^{-2}$

Since, the change of momentum obtained is per unit time, it is same as the force.  

Thus, the force acting on the wall by water $=$ force experienced by water jet$=400 \mathrm{N}$.