Question

A stream of water flowing horizontally with a speed of $15m{s}^{-1}$ gushes out of a tube of cross-sectional area ${10}^{-2}{m}^2$, and hits a vertical wall normally. Assuming that it does not rebound from the wall, the force exerted on the wall by the impact of water is:

• A. $1.25\times {10}^{3}N$
• B. $2.25\times {10}^{3}N$
• C. $3.25\times {10}^{3}N$
• D. $4.25\times {10}^{3}N$

Answer 1

Answer: (B)

$2.25\times {10}^{3}N$

Here, $v=15m{s}^{-1}$
Area of cross section, $A={10}^{-2}{m}^2$
Density of water, $\rho ={10}^{3}kg{m}^{-3}$
Mass of water hitting the wall per second
=$\rho \times A\times v$

=${10}^{3}kg{m}^{-3}\times {10}^{-2}{m}^2\times 15m{s}^{-1}=150kg{s}^{-1}$

Force exerted on the wall= Momentum loss of water per second

=$150kg{s}^{-1}\times 15m{s}^{-1}=2250N=2.25\times {10}^{3}N$