Empty the barrel

Classical Mechanics Level 3

Two identical barrels with identical valves at the bottom are placed on a table so that the water can freely flow to the ground. The first barrel is filled with hot water, the second one is filled with cold water. If we open the valves at the same time, which one of the barrels will be empty first?

The one with hot water will be first, because hot water has smaller viscosity than cold water The one with cold water will be first, because cold water is denser than hot water. The will be empty at about the same time

Laszlo Mihaly by Laszlo Mihaly , 57, USA

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1 solution

Laszlo Mihaly
Dec 9, 2018

The flow through the valve is turbulent, because the Reynolds number will be in the order of 100,000 (except for the very end of the flow, when the velocity of the water is very small). When the flow is turbulent, the viscosity does not matter. The two containers will be empty at the same time.

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