Question 1

Which of the following statements about friction is correct?

Accepted Answer

Friction is measured by the coefficient of friction and is independent of contact area.

Question 2

A 10 kg box rests on a horizontal floor. The coefficient of static friction between the box and the floor is $$\mu_s = 0.4. $$What is the maximum force that can be applied horizontally before the box starts to move?

Accepted Answer

$$39.2\,\mathrm{N}$$

Question 3

Which equation correctly gives the magnitude of the kinetic friction force acting on an object sliding on a flat surface?

Accepted Answer

$$f_k = \mu_k F_N$$

Question 4

A person pushes a 15 kg sled with a force of $$80\,\mathrm{N} at$$ $$30^\circ$$ below the horizontal. The coefficient of kinetic friction is $$\mu_k = 0.1. $$What is the horizontal component of the applied force?

Accepted Answer

$$69.28\,\mathrm{N}$$

Question 5

In the context of walking, what role does friction play?

Accepted Answer

Friction enables the person to push backward on the ground, resulting in forward acceleration.

Question 6

A block is pushed with increasing force. It does not move at 10 N or 25 N, but starts to slide at 26 N. Which statement is correct?

Accepted Answer

The maximum static friction is between 25 N and 26 N.

Question 7

A 20 kg box is pulled across a floor with a constant velocity by a horizontal force. If the coefficient of kinetic friction is $$\mu_k = 0.2$$, what is the magnitude of the pulling force?

Accepted Answer

$$39.2\,\mathrm{N}$$

Question 8

Which of the following is true about the direction of friction and normal forces when an applied force is angled downward on a box?

Accepted Answer

The normal force increases and friction force increases.

Question 9

A chandelier of mass $$80\,\mathrm{kg}$$ hangs motionless from the ceiling by two ropes, each making a $$60^\circ$$ angle with the ceiling. What is the tension in each rope?

Accepted Answer

$$452\,\mathrm{N}$$

Question 10

Which of the following best describes the relationship between static and kinetic friction coefficients?

Accepted Answer

$$\mu_s \geq \mu_k$$

Question 11

A car accelerates forward on a road. What is the direction of the friction force exerted by the road on the tires?

Accepted Answer

Forward, in the direction of the car's acceleration.

Question 12

If a box is at rest and a horizontal force is applied but does not move the box, what can be said about the static friction force?

Accepted Answer

It is equal in magnitude and opposite in direction to the applied force.

Question 13

A 5 kg block is pulled with a force of $$30\,\mathrm{N} at$$ $$20^\circ$$ above the horizontal. The coefficient of kinetic friction is $$\mu_k = 0.3. $$What is the net horizontal acceleration of the block? (Use $$g = 9.8\,\mathrm{m/s^2$})$$

Accepted Answer

$$2.1\,\mathrm{m/s^2$}$$

Question 14

Which of the following is NOT a property of friction as described in the study materials?

Accepted Answer

Friction increases significantly if the contact surfaces deform.

Question 15

In a static equilibrium problem involving two ropes holding a mass, which of the following statements is true?

Accepted Answer

The horizontal components of the tensions in the two ropes are equal in magnitude and opposite in direction.

Question 16

A 12 kg crate is at rest on a horizontal surface. The coefficient of static friction is $$\mu_s = 0.5. $$What is the minimum horizontal force required to start moving the crate?

Accepted Answer

$$58.8\,\mathrm{N}$$

Question 17

If the applied force on a box is less than the maximum static friction, what happens?

Accepted Answer

The box remains at rest.

Question 18

Which of the following best explains why it is harder to start moving a heavy object than to keep it moving?

Accepted Answer

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

Question 19

A 25 kg box is pulled with a force of $$100\,\mathrm{N} at$$ $$45^\circ$$ above the horizontal. The coefficient of kinetic friction is $$\mu_k = 0.2. $$What is the normal force acting on the box? (Use $$g = 9.8\,\mathrm{m/s^2$})$$

Accepted Answer

$$174.3\,\mathrm{N}$$

Friction and Newton's Second Law: Forces and Applications

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