# Worksheet: Stokes' Law

In this worksheet, we will practice calculating the friction force acting on a sphere as it travels through a viscous fluid.

**Q1: **

What is the magnitude of the force due to fluid friction exerted on a sphere of radius 15 cm that moves horizontally at 15 cm/s through water of dynamic viscosity Pa⋅s?

**Q2: **

A sphere of radius 12 cm moves horizontally at 20 cm/s through a liquid that produces a fluid friction force of magnitude 240 μN. What is the dynamic viscosity of the liquid?

- A Pa⋅s
- B Pa⋅s
- C Pa⋅s
- D Pa⋅s
- E Pa⋅s

**Q3: **

Which of the following formulas correctly relates , the fluid friction force; , the dynamic viscosity; , the radius of a sphere; and , the velocity with which the sphere moves through the fluid?

- A
- B
- C
- D
- E

**Q4: **

A solid sphere moves vertically downward through water at a constant velocity , as shown in the diagram. The forces acting on the sphere are its weight, , the upthrust from the water, , and the fluid friction due to the water, . Which of the following equations correctly shows the relation of these forces to each other?

- A
- B
- C
- D
- E

**Q5: **

A solid sphere of radius 1.5 cm
and density 1,050 kg/m^{3}
moves vertically downward through a liquid at a constant velocity , as shown in the diagram. The density of the liquid is 975 kg/m^{3}.
Find the dynamic viscosity of the liquid.