Physics - Center of Mass Question with Solution | TestHub

The mass of water striking the wall per unit time is $\frac{dm}{dt}=\rho Av$. The initial momentum per unit time of the water stream is $p_{initial}=(\frac{dm}{dt})v=(\rho Av)v=\rho A{v}^2$. Since the water comes to rest, its final momentum is zero. The force exerted by the water on the wall is equal to the rate of change of momentum of the water. Therefore, $F=\frac{\Delta p}{\Delta t}=p_{initial}-p_{final}=\rho A{v}^2-0=\rho A{v}^2$.