Engineering
Physics
Statics
Question

A stopper is used to block a small hole at the base of a vessel. Force exerted by liquid on stopper is F1. The stopper is then removed. Force experienced by vessel due to issuing liquid now is F2 neglect atmospheric pressure, F1/F2 =?

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Solution

When the stopper blocks the hole, the force F1 is simply the hydrostatic pressure at depth h times the area A of the hole. Since pressure P = ρgh, we get F1 = ρghA.

After removal, the liquid issues out. The force F2 on the vessel is the rate of change of momentum of the issuing liquid. Using Torricelli's theorem, the speed of efflux v = √(2gh). The mass flow rate is dm/dt = ρAv. The force F2 = (dm/dt)v = ρA(2gh).

Therefore, the ratio F1/F2 = (ρghA) / (2ρghA) = 1/2.

Final Answer: 12