Question

A steam of water flowing horizontally with a speed of $20ms^{- 1}$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. 125 N
• B. 625 N
• C. -650 N
• D. -1125 N

Answer 1

Answer: (B)

625 N

Answer 2

Here, $u = 25ms^{- 1},v = 0,t = 1,A = 10^{- 3}m^{2}$

Density of water $\rho = 1000kgm^{- 3}$

Mass of water gushed out per second,

m = $\frac{volume \times density}{time} = \frac{area \times dis\tan ce \times density}{time}$

$= Area \times velocity \times density$

$= Av\rho = 10^{- 3} \times 25 \times 1000 = 25kg$

Force exerted on the wall by the impact of water

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

$F' = - F = 625N$