Viscous drag and Stokes' law Quiz
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5 questions, one answer each
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1. A sphere of radius 2.0 mm moves at 0.10 m s⁻¹ through a liquid of viscosity 0.50 Pa s. What is the drag force?
- A. 1.9 × 10⁻³ N
- B. 6.0 × 10⁻⁴ N
- C. 3.8 × 10⁻³ N
- D. 1.9 × 10⁻⁶ N
2. Which condition is NOT needed for Stokes' law to apply?
- A. Small sphere
- B. Low speed
- C. Laminar flow
- D. Fluid at constant temperature of 20 °C
3. A ball falls at terminal velocity in oil. Which statement is correct?
- A. Weight = upthrust + drag
- B. Weight = drag only
- C. Upthrust = drag
- D. Weight is less than the upthrust
4. The temperature of a liquid is increased. Why does a ball then fall faster through it?
- A. The liquid becomes denser
- B. The viscosity of the liquid decreases, so there is less drag at a given speed
- C. The ball's mass increases
- D. The upthrust increases greatly
5. In the falling-ball method a student times a ball from the moment it is released at the surface. What is the effect on the calculated viscosity?
- A. It is too low, because the average speed is too high
- B. It is unaffected
- C. It is too high, because the average speed is lower than the terminal velocity
- D. It is zero