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

In partnership with Revision Ninja

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.

Host it live on the board and students join with a game code on their own devices, or revise alone with Free Play. The answers are revealed in the game.

Host this setFree Play

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. Under which conditions does Stokes' law apply?

    • Objects of any shape moving at any speed
    • Small spherical objects moving at low speeds in laminar flow
    • Large spherical objects moving at high speeds in turbulent flow
    • Objects moving at speeds above the speed of sound in the fluid

  3. What is meant by the viscosity of a liquid?

    • Its ability to conduct electric current
    • The upthrust acting on a body placed in it
    • Its resistance to flow, arising from internal friction between layers of the liquid
    • Its density per unit volume

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

    • It stays the same
    • It decreases
    • It increases in direct proportion to the absolute temperature
    • It increases

  5. A sphere falling through a viscous fluid reaches terminal velocity. What is true at that point?

    • Its acceleration is at a maximum
    • The net force on it is zero, so drag plus upthrust balances its weight
    • The drag force on it is zero
    • Its weight is zero

  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. A student uses Stokes' law to calculate drag on a large raindrop falling at 10 m/s through air. What is the best evaluation?

    • Stokes' law applies, because air is a viscous fluid at any speed
    • Stokes' law applies, but only with a different constant for air
    • Stokes' law does not apply, because the drop is not small and the flow at this speed is turbulent
    • Stokes' law applies, because raindrops are spherical

  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. A student says that a falling sphere's terminal velocity depends only on its mass. Which evaluation is correct?

    • The claim is right, because heavier objects always fall faster through any fluid
    • The claim is wrong, because terminal velocity does not depend on the fluid at all
    • The claim is right, because drag depends only on the mass of the sphere
    • The claim is wrong, because terminal velocity depends on radius, density difference and the fluid's viscosity

  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. Why must temperature be controlled in a falling-ball viscosity experiment?

    • Stokes' law is valid only at one fixed temperature for every fluid
    • Temperature changes the mass of the ball, so its weight changes during the fall
    • The viscosity of a liquid depends strongly on temperature, so the terminal velocity and calculated viscosity would change
    • Temperature changes the value of g in the laboratory

All Pearson Edexcel Physics quizzes