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A student wishes to find the velocity of air flowing through a pipe. He has a pressure gauge which displays only the dynamic pressure. The pressure gauge reads 0.018 mm Hg. Assume density of air to be 1.225 kg/m^3, find the velocity V of air (ρHg = 13600 kg/m^3).

(a) 4 m/s

(b) 2 m/s

(c) 20 m/s

(d) 40 m/s

I have been asked this question during an interview.

Question is from Introduction to Fluid Dynamics topic in portion Fluid Dynamics of Fluid Mechanics

1 Answer

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Best answer
The correct option is (b) 2 m/s

Easiest explanation: (0.018 mm Hg * 13.6 * 9.8) = 2.4 bar. Dynamic pressure is given by ρV^2/2. Equating 2.4 bar with dynamic pressure gives V = 2 m/s.

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