Lesson 4.1.2

4.1.2 Viscous drag and Stokes' law Quiz: Pearson Edexcel Physics, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.1.2, Viscous drag and Stokes' law: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 4: Materials, written with Revision Ninja.

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The 20 questions

  1. Which equation is Stokes' law for the viscous drag on a small sphere?

    • F = 6 pi eta r v
    • F = 3 pi eta r v^2
    • F = 6 pi eta r^2 v
    • F = 4 pi eta r v^2

  2. Which type of fluid flow is required for Stokes' law to be valid?

    • Compressible flow
    • Laminar flow
    • Turbulent flow
    • Rotational flow

  3. What physical property describes a liquid's internal resistance to flow?

    • Surface tension
    • Stiffness
    • Viscosity
    • Density

  4. How does the viscosity of a liquid change as its temperature increases?

    • It stays constant
    • It decreases
    • It becomes zero
    • It increases

  5. When a sphere falling through a fluid reaches terminal velocity, what is the resultant force?

    • Equal to drag
    • Zero
    • Equal to weight
    • Equal to upthrust

  6. What is the SI unit of viscosity?

    • N m
    • Pa s
    • kg m s^-1
    • m s^-2

  7. A small sphere of radius r and density rho_s falls at terminal velocity v through a fluid of density rho_f and viscosity eta. Which expression gives v?

    • v = 2 r^2 (rho_s - rho_f) g/(9 eta)
    • v = 9 r^2 (rho_s - rho_f) g/(2 eta)
    • v = 2 r (rho_s - rho_f) g/(9 eta)
    • v = 2 r^2 (rho_s + rho_f) g/(9 eta)

  8. A sphere of radius 2.0 mm moves at 0.050 m/s through a liquid of viscosity 0.80 Pa s. What is the viscous drag on it?

    • 3.0 x 10^-2 N
    • 1.5 x 10^-3 N
    • 6.0 x 10^-4 N
    • 3.0 x 10^-3 N

  9. A steel sphere of radius 1.0 mm (density 2700 kg/m^3) falls through a liquid of density 1000 kg/m^3 and viscosity 1.0 Pa s. What is its terminal velocity? Take g = 9.8 N/kg.

    • 7.4 x 10^-3 m/s
    • 3.7 x 10^-1 m/s
    • 1.9 x 10^-2 m/s
    • 3.7 x 10^-3 m/s

  10. If the radius of a sphere falling at terminal velocity in a fixed fluid is doubled, by what factor does its terminal velocity change?

    • 4 times greater
    • 2 times greater
    • 8 times greater
    • Unchanged

  11. At terminal velocity a sphere has weight 0.050 N and upthrust 0.020 N. What is the drag force on it?

    • 0.030 N
    • 0.070 N
    • 0.020 N
    • 0.050 N

  12. A sphere falls at a constant terminal velocity of 0.20 m/s. How long does it take to fall 0.50 m at this speed?

    • 0.40 s
    • 0.10 s
    • 10 s
    • 2.5 s

  13. In a falling-ball experiment, a sphere of radius 0.50 mm, with density difference 1500 kg/m^3 from the liquid, falls at terminal velocity 0.0040 m/s. What is the viscosity of the liquid? Take g = 9.8 N/kg.

    • 0.020 Pa s
    • 0.20 Pa s
    • 0.0020 Pa s
    • 2.0 Pa s

  14. The drag on a sphere moving at 0.10 m/s in a fluid of viscosity 0.10 Pa s is 0.00377 N. What is the radius of the sphere?

    • 2.0 cm
    • 20 m
    • 0.20 cm
    • 2.0 mm

  15. A sphere moving slowly through a fluid has drag 0.0030 N at speed 0.10 m/s. If its speed doubles to 0.20 m/s, staying in laminar flow, what is the new drag?

    • 0.0030 N
    • 0.0120 N
    • 0.0060 N
    • 0.0015 N

  16. Why does Stokes' law fail for a large raindrop falling at high speed?

    • Air is incompressible
    • Upthrust is zero
    • Flow is turbulent
    • Flow is laminar

  17. A steel ball of radius 1.0 mm falls at constant speed 0.40 m/s in a liquid. Its density difference from the liquid is 6600 kg/m^3. What is the viscosity of the liquid? Take g = 9.8 N/kg.

    • 3.6 Pa s
    • 0.0036 Pa s
    • 0.36 Pa s
    • 0.036 Pa s

  18. Under Stokes' law, terminal velocity is directly proportional to which variable?

    • Radius
    • Viscosity squared
    • Mass squared
    • Radius squared

  19. A sphere of radius 0.50 mm and density 2500 kg/m^3 falls through oil of density 900 kg/m^3 and viscosity 0.50 Pa s. What is its terminal velocity? Take g = 9.8 N/kg.

    • 0.17 mm/s
    • 17 mm/s
    • 3.5 mm/s
    • 1.7 mm/s

  20. Which property changes significantly when temperature varies during a falling-ball experiment?

    • Sphere density
    • Ball radius
    • Liquid viscosity
    • Gravitational field

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