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External mouthpiece: pressure at vena contracta relative to atmosphere In a free-discharging external mouthpiece, the absolute pressure head at the vena contracta is ____ the atmospheric pressure head by approximately 0.89 times the height of liquid above the vena contracta. Choose the correct completion.

Difficulty: Medium

equal to
greater than
less than
independent of

Correct Answer: less than

Explanation:

Concept/Approach

At the vena contracta of an external mouthpiece, the jet accelerates and the static pressure drops below atmospheric. Experiments show the pressure deficit is about 0.89h, where h is the liquid height above the vena contracta.

Final Answer
less than

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