Worksheet: Static Friction

In this worksheet, we will practice analyzing the forces acting on objects on frictional surfaces that are required to induce motion in the objects.

Q1:

A brick is initially at rest on top of a rough horizontal surface, as shown in the diagram. The brick is pushed by a force F = 2 5 N parallel to the surface and starts to move. The weight of the brick 𝑊 = 2 8 N . What must the coefficient of static friction of the brick with the surface be less than?

Q2:

The figure shows two blocks, block A and block B. Block A is on a rough surface, and block B is on block A. A force 𝐹 acts on block A, parallel to the surface. Initially, block A does not move, and 𝐹 is steadily increased. When 𝐹 has increased enough to make block A start to move, both blocks move in the direction of 𝐹 , but block A has a greater acceleration than block B. Which of the following is a correct statement about the relation of 𝜇 , the coefficient of static friction between block A and the surface, to 𝜇 , the coefficient of static friction between the blocks?

  • A 𝜇 < 𝜇
  • B 𝜇 > 𝜇
  • C 𝜇 = 𝜇

Q3:

A brick is initially at rest on top of a rough horizontal surface, as shown in the diagram. The brick is pushed by a force F = 2 2 N parallel to the surface and starts to move. The coefficient of static friction of the brick with the surface is 0.75. What must the weight of the brick, 𝑊 , be less than?

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