Q: A box of mass $$m = 103.7\ \mathrm{kg}$$ rests on a floor with a coefficient of kinetic friction $$\mu_k = 0.37. $$What is the minimum force required to keep the box moving at constant velocity? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

$$F = 103.7 \times 9.8 \times 0.37 = 376.6\ \mathrm{N}$$

Q: If the coefficient of friction between a tire and dry asphalt is $$\mu = 0.8$$, what is the maximum horizontal force that can be applied to a $$1500\ \mathrm{kg}$$ car before it starts to skid? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

$$F_{max} = 1500 \times 9.8 \times 0.8 = 11760\ \mathrm{N}$$

Q: A person pushes a box with a force of $$500\ \mathrm{N}$$, but the box does not move. The normal force is $$1000\ \mathrm{N}$$ and the coefficient of static friction is $$0.6. $$What is the maximum static friction force?

$$F_{s,max} = 1000 \times 0.6 = 600\ \mathrm{N}$$

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 kinetic friction $$\mu_k = 0.37. $$What is the minimum force required to keep the box moving at constant velocity? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$F = 103.7 	imes 9.8 	imes 0.37 = 376.6\ \mathrm{N}$$

Question 3

Which equation correctly relates the frictional force $$F_f to $$the normal force $$N$$ and the coefficient of friction $$\mu$$?

Accepted Answer

$$F_f = \mu N$$

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 it takes more force to overcome the initial interlocking of surface irregularities than to keep them sliding.

Question 5

A person tries to push a heavy wardrobe but it does not move. Which type of friction is acting between the wardrobe and the floor?

Accepted Answer

Static friction

Question 6

If the normal force between two surfaces is doubled, what happens to the maximum possible frictional force?

Accepted Answer

It is doubled.

Question 7

A car is parked on a hill. Which type of friction prevents it from sliding down?

Accepted Answer

Static friction

Question 8

Which of the following scenarios best illustrates kinetic friction?

Accepted Answer

A sled sliding down a snowy hill.

Question 9

A student claims that friction always acts to slow down objects. Which of the following real-world examples contradicts this claim?

Accepted Answer

A person walking forward due to friction between shoes and ground.

Question 10

If the coefficient of friction between a tire and dry asphalt is $$\mu = 0.8$$, what is the maximum horizontal force that can be applied to a $$1500\ \mathrm{kg}$$ car before it starts to skid? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$F_{max} = 1500 	imes 9.8 	imes 0.8 = 11760\ \mathrm{N}$$

Question 11

Which of the following statements about the coefficient of friction is correct?

Accepted Answer

It is a property of the two surfaces in contact.

Question 12

A person pushes a box with a force of $$500\ \mathrm{N}$$, but the box does not move. The normal force is $$1000\ \mathrm{N}$$ and the coefficient of static friction is $$0.6. $$What is the maximum static friction force?

Accepted Answer

$$F_{s,max} = 1000 	imes 0.6 = 600\ \mathrm{N}$$

Question 13

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

Accepted Answer

Using smoother surfaces.

Question 14

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

Accepted Answer

The applied force is equal to the frictional force.

Question 15

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

Accepted Answer

Magnetic friction

Question 16

A block is at rest on a horizontal surface. Which force balances the weight of the block?

Accepted Answer

Normal force

Question 17

If a box is moving and suddenly stops, which type of friction is responsible for bringing it to rest?

Accepted Answer

Kinetic friction

Question 18

A person pushes a box across a floor. If the coefficient of friction increases, what happens to the force required to keep the box moving at constant velocity?

Accepted Answer

The required force increases.

Question 19

Which of the following best explains why car tires are designed with tread patterns?

Accepted Answer

To increase friction and prevent slipping, especially on wet surfaces.

Friction: Concepts, Types, and Applications

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