Question

A steam of water flowing horizontally with a speed of $25m{s}^{-1}$ gushes out of a tube of cross-sectional area ${10}^{-3}{m}^2$, and hits at a vertical wall nearby. What is the force exerted on the wall by the impact of water?

• A. $125N$
• B. $625N$
• C. $-650N$
• D. $-1125N$

Answer 1

Answer: (B)

$625N$

Here, $u=25m{s}^{-1},v=0,t=1s,A={10}^{-3}{m}^2$
Density of water, $rho=1000kg{m}^{-3}$

Mass of water gushed out per second, m =$\frac{volume\times density}{time}=\frac{area\times distance\times density}{time}$

= $Area\times velocity\times density$

$=Av\rho ={10}^{-3}\times 25\times 1000=25kg$
Force exerted on the wall by the impact of water,

$F=ma=m\left(\frac{v-u}{t}\right)=25\times \left(\frac{-2}{1}\right)=625N$

F'=-F= 625 N