Question
A stream of water flowing horizontally with a speed of 15 m s–1 gushes out of a tube of cross-sectional area 10–2m2, and hits a vertical wall nearby. What is the force exerted on the wall by the impact of water, assuming it does not rebound?
Solution
Given,
Speed of the water stream, v = 15 m/s
Cross-sectional area of the tube, A = 10–2 m2Speed of the water stream, v = 15 m/s
Volume of water coming out from the pipe per second,
V = Av
= 15 × 10–2 m3/s
Density of water, ρ = 103 kg/m3
Mass of water flowing out through the pipe per second = ρ ×V
= 150 kg/s
The water strikes the wall and does not rebound.
Therefore, according to Newton's second law of motion,
Force exerted by the water on the wall,
F = Rate of change of momentum =
=
= 150 × 15
= 2250 N
