# 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/m3 moves vertically downward through a liquid at a constant velocity , as shown in the diagram. The density of the liquid is 975 kg/m3. Find the dynamic viscosity of the liquid.

Q6:

A sphere of radius 7.5 cm and density 1,500 kg/m3 moves horizontally through water of dynamic viscosity Pa⋅s. The sphere is decelerating at m/s2. What is the magnitude of the velocity of the sphere?

Q7:

A solid sphere of radius 1.1 cm and density 1,095 kg/m3 moves vertically downward through a liquid of dynamic viscosity Pa⋅s and density 1,025 kg/m3, as shown in the diagram. Find the velocity of the sphere.

Q8:

A solid sphere of radius 6.200 mm moves vertically downward at a constant velocity cm/s through a liquid of dynamic viscosity Pa⋅s and density 1,025 kg/m3, as shown in the diagram. Find the density of the sphere.

Q9:

A positively charged solid sphere is placed within a fluid. The fluid is within a cylindrical container that has oppositely charged circular faces, as shown in the diagram. The sphere moves vertically upward with a constant velocity cm/s. The sphere has a radius of 2.2 cm and a density of 1,500 kg/m3. The fluid has a density of 1,450 kg/m3 and a dynamic viscosity of Pa⋅s. What is the ratio of the magnitude of the electric force acting on the sphere to the magnitude of the drag force acting on the sphere?