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)

Here, $u=25$ $m{s}^{-1},$ $v=0,$ $t=1s,$ $A=10^{-3}$ $m^2$
Density of water, $\rho =1000kg$ $m^{-3}$
Mass of water gushed out per second, $m$
$=\frac{volume\times density}{time}=\frac{area\times distance\times density}{time}$
$=Area\times velocity\times density$
$=A\nu \rho =10^{-3}$ $\times 25\times 1000=25kg$
Force exerted on the wall by the impact of water,
$F=ma$ $=m$ $\left(\frac{v-u}{t}\right)$ $=25\times \left(\frac{-25}{1}\right)$ $=-625N$
$F^{\prime }$ $=-F=625N$