Question

A flat plate moves normally towards a discharging jet of water at the rate of $3m/s$. The jet discharges the water at the rate of $0.1m^3/s$ and at the speed of $18m/s$. The force exerted on the plate due to the jet is :

• A. $1800N$
• B. $2100N$
• C. $2450N$
• D. $1560N$

Answer 1

The correct option is B $2100N$

Force experienced by plate$=$ Rate of change of momentum of plate.

Change in $\overrightarrow{V}$ of water $=21m/s$

Change in momentum per second $=\frac{\left(mass\right)\left(\Delta V_1\right)}{time}$

Rate of water discharge $=0.1m^3/sec$

Rate of water discharge $=0.1\times {10}^{3}kg/sec={10}^{2}kg/sec$

$\Rightarrow$ Change in momentum per second $={10}^2\times 21=2100$

Force experienced by plate $=2100N$