Question

A liquid of density $\rho$ is coming out of a hose pipe of radius a with horizontal speed $v$ and hits a mesh. $50\%$ of the liquid passes through the mesh unaffected. $25\%$ looses all of its momentum and $25\%$ comes back with the same speed. The resultant pressure on the mesh will be :

• A. $pv^2$
• B. $\frac{3}{4} pv^2$
• C. $\frac{1}{2} pv^2$
• D. $\frac{1}{4} pv^2$

Answer 1

Answer: (B)

Momentum per second carried by liquid per second is $\rho av^2$
net force due to reflected liquid = $2 \times [ \frac{1}{4} \rho av^2 ]$
net force due to stopped liquid = $\frac{1}{4} \rho av^2$
Total force = $\frac{3}{4} \rho av^2$
net pressure = $\frac{3}{4} \rho v^2$