Question

Water coming out of a horizontal tube at a speed $v$ strikes normally to the vertical wall 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 striking the wall will also be four times.
• D. The energy lost per second by water striking the wall be increased by 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 be increased by eight times.

Thrust = Rate of charge of linear momentum
Thrust $=\rho Av(v-0)=\rho A{v}^2$
If velocity is doubled then thrust will increase four times.

Energy lost per second $=\frac{1}{2}m{v}^2=\frac{1}{2}\rho A{v}^3$

If velocity is doubled then energy lost per second will be eight times.