Question

A stream of water of density d, cross-section A and speed v strikes a wall that is perpendicular to the stream as shown. The water then flows sideways along the wall. The force exerted by the stream on the wall is -

• A. dv²A
• B. dvA/2
• C. dghA
• D. v²A/d

Answer 1

Answer: (A)

dv²A

Answer 2

The mass of water reaching the wall per second

= v Ad.

the momentum transferred per second = (vAd)v

̃ $\overrightarrow { \mathrm { p } }$ per unit time = v² Ad.

The flow of water , tangential to the wall does not contribute to the force.

Therefore, force = rate of change of momentum

= v² Ad.