Question

A jet of water having velocity$=10m/s$ and stream cross-section$=2{cm}^2$ hits a flat plate perpendicularly, with the water splashing out parallel to plate. The force imparted by the jet on the plate is $10\times x$. Find the value of $x$.

Answer 1

Rate of volume of liquid hitting the plate $=av$
Rate of mass hitting the plate $=\rho av$

Since after hitting the plate the water splits parallel to the plate, hence final momentum will be 0 by symmetry.
Rate of momentum transferred to the plate $=F=\rho av\times v=\rho a{v}^2$
$\Rightarrow F=1000\times \frac{2}{100\times 100}\times {10}^2=20N$

Hence value of $x$ is $2$