Question

Water coming out of a horizontal tube at a speed $v$ strikes normally a vertically was close to the mouth of the tube and falls down vertically after impact. When the speed of water is increased to $2v$.

• A. the thrust exerted by the water on the wall will be doubled
• B. the thrust exerted by the water on the wall will be four times
• C. the energy lost per second by water strikeup the wall will also be four times
• D. the energy lost per second by water striking the wall will be increased eight times

Answer 1

Answer: (B), (D)

The correct options are
B the thrust exerted by the water on the wall will be four times
D the energy lost per second by water striking the wall will be increased eight times

Initial thrust F=$\rho A{v}^2$

when velocity is doubled thrust =$\rho A\left(2v^2\right)=4F$

energy lost E=$\rho Av\times (v{)}^2/2$

Energy lost $=\rho A2v\times (2v{)}^2/2=8E$