Q: A box of mass $$m = 103.7\ \mathrm{kg}$$ rests on a floor with a coefficient of static friction $$\mu_s = 0.37. $$What is the minimum force required to start moving the box?

$$F = 103.7 \times 9.8 \times 0.37 = 376.98\ \mathrm{N}$$

Q: If the coefficient of kinetic friction between a box and the floor is $$\mu_k = 0.25$$ and the normal force is $$N = 500\ \mathrm{N}$$, what is the kinetic friction force?

$$F_k = 0.25 \times 500 = 125\ \mathrm{N}$$

Question 1

Which of the following best describes the direction of the frictional force acting on an object sliding across a horizontal surface?

Accepted Answer

Friction acts opposite to the direction of the object's motion.

Question 2

A box of mass $$m = 103.7\ \mathrm{kg}$$ rests on a floor with a coefficient of static friction $$\mu_s = 0.37. $$What is the minimum force required to start moving the box?

Accepted Answer

$$F = 103.7 	imes 9.8 	imes 0.37 = 376.98\ \mathrm{N}$$

Question 3

Which statement about the coefficient of friction $$\mu is $$correct?

Accepted Answer

$$\mu is $$the ratio of the frictional force to the normal force.

Question 4

Why is the coefficient of static friction usually greater than the coefficient of kinetic friction for the same pair of surfaces?

Accepted Answer

Because static friction involves microscopic interlocking that must be overcome to initiate motion.

Question 5

A person pushes a box across a floor at constant velocity. Which statement is true about the forces acting on the box?

Accepted Answer

The applied force is equal to the kinetic friction force.

Question 6

If the normal force $$N$$ acting on an object is doubled, what happens to the maximum static friction force $$F_{s,\mathrm{max}}$$?

Accepted Answer

$$F_{s,\mathrm{max}} is $$doubled.

Question 7

Which of the following real-life scenarios best illustrates the role of static friction?

Accepted Answer

A person standing still on a sloped sidewalk without sliding.

Question 8

Given the equation for frictional force $$F_f = \mu N$$, which variable would increase if the surface became rougher?

Accepted Answer

$$\mu$$, the coefficient of friction

Question 9

A student claims that friction always acts to slow down objects. Which situation disproves this claim?

Accepted Answer

A car accelerating forward due to friction between its tires and the road.

Question 10

A box is at rest on a horizontal surface. Which force is responsible for preventing the box from moving when a small horizontal force is applied?

Accepted Answer

Static friction

Question 11

If the coefficient of kinetic friction between a box and the floor is $$\mu_k = 0.25$$ and the normal force is $$N = 500\ \mathrm{N}$$, what is the kinetic friction force?

Accepted Answer

$$F_k = 0.25 	imes 500 = 125\ \mathrm{N}$$

Question 12

Which of the following would decrease the frictional force between two surfaces?

Accepted Answer

Using a lubricant between the surfaces

Question 13

A person pushes a box with a force of $$400\ \mathrm{N}$$, but the box does not move. The normal force is $$1000\ \mathrm{N}$$ and the coefficient of static friction is $$0.45. $$What is the maximum static friction force?

Accepted Answer

$$F_{s,\mathrm{max}} = 0.45 	imes 1000 = 450\ \mathrm{N}$$

Question 14

Which of the following is NOT a type of friction discussed in the study materials?

Accepted Answer

Fluid friction

Question 15

A car is parked on a hill. Which force prevents it from sliding down?

Accepted Answer

Static friction

Question 16

If the coefficient of friction between two surfaces is zero, what happens when a horizontal force is applied to an object resting on the surface?

Accepted Answer

The object will move with no resistance.

Question 17

Which equation correctly represents the frictional force acting on an object?

Accepted Answer

$$F_f = \mu N$$

Question 18

A person pushes a box across a floor. If the box moves at a constant velocity, what can be said about the net force acting on the box?

Accepted Answer

The net force is zero.

Question 19

Which of the following best explains why it is easier to keep an object moving than to start it moving?

Accepted Answer

The coefficient of kinetic friction is less than the coefficient of static friction.

Friction: Concepts, Types, and Applications

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