Answer: 9 : 1.
- A 3 : 1
- B 6 : 1
- C 9 : 1
- D 27 : 1
Correct answer: C. 9 : 1
Explanation: Terminal velocity ∝ r<sup>2</sup> (Stokes), so the ratio is 3<sup>2</sup> : 1 = 9 : 1.
Since the same volume of fluid must pass every cross-section per second (continuity), the fluid speeds up where the pipe narrows; Bernoulli's equation then says this faster-moving fluid has lower pressure - the principle behind a venturi meter and an aircraft wing's lift.
Concept context
Pressure, buoyancy, Bernoulli equation, viscosity, and surface tension.