Answer: 4×.
- A 2×
- B 4×
- C 8×
- D unchanged
Correct answer: B. 4×
Explanation: Terminal velocity ∝ r², so doubling the radius multiplies it by 4.
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.