In the mass flow rate equation, hL represents which quantity?

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Multiple Choice

In the mass flow rate equation, hL represents which quantity?

Explanation:
Gravity-driven flow is governed by the head of liquid above the outlet. The driving pressure at the hole comes from the weight of the liquid column above it, which is determined by the vertical distance from the free surface down to the outlet. This height, hL, sets the exit velocity through v ≈ sqrt(2 g hL) (ignoring losses), and thus influences the mass flow rate. So hL is the height between the hole in the tank and the top of the liquid, not simply the overall liquid depth or the outlet’s own height.

Gravity-driven flow is governed by the head of liquid above the outlet. The driving pressure at the hole comes from the weight of the liquid column above it, which is determined by the vertical distance from the free surface down to the outlet. This height, hL, sets the exit velocity through v ≈ sqrt(2 g hL) (ignoring losses), and thus influences the mass flow rate. So hL is the height between the hole in the tank and the top of the liquid, not simply the overall liquid depth or the outlet’s own height.

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