Q: A block is on the verge of slipping down an incline. If the angle of the incline is $$\theta$$ and the coefficient of static friction is $$\mu_s$$, what is the minimum angle $$\theta_{min}$$ for slipping to occur?

$$\theta_{min} = \arctan(\mu_s)$$

Question 1

A 10 kg box is at rest on a horizontal surface. A horizontal force of 30 N is applied, but the box does not move. If the coefficient of static friction between the box and the surface is $$\mu_s = 0.4$$, what is the magnitude of the frictional force acting on the box?

Accepted Answer

$$30\ \mathrm{N}$$

Question 2

Which of the following statements best describes Newton's First Law of Motion?

Accepted Answer

An object will remain at rest or move with constant velocity unless acted upon by a net external force.

Question 3

A 70 kg astronaut weighs less on the Moon than on Earth. Which of the following quantities is the same on both the Moon and Earth?

Accepted Answer

The astronaut's mass

Question 4

A 5 kg block is pulled across a horizontal surface with a constant velocity by a force of 20 N. What is the coefficient of kinetic friction between the block and the surface? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$0.41$$

Question 5

A car accelerates forward. According to Newton's Third Law, what is the reaction force to the force that the car's tires exert on the road?

Accepted Answer

The road exerts an equal and opposite force on the car's tires.

Question 6

A 2 kg block is placed on a frictionless incline of $$30^\circ. $$What is the magnitude of the normal force acting on the block?

Accepted Answer

$$16.97\ \mathrm{N}$$

Question 7

A 3 kg object is suspended by a rope. What is the tension in the rope if the object is at rest? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$29.4\ \mathrm{N}$$

Question 8

A 4 kg block is sliding down a rough incline at a constant speed. The incline makes an angle of $$25^\circ$$ with the horizontal. What is the coefficient of kinetic friction between the block and the incline? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$0.47$$

Question 9

Which of the following is NOT a contact force?

Accepted Answer

Gravitational force

Question 10

A 10 kg box is at rest on a horizontal surface. What is the normal force acting on the box? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$98\ \mathrm{N}$$

Question 11

A 2 kg block is pulled by a rope with a force of 15 N at an angle of $$30^\circ$$ above the horizontal. If the coefficient of kinetic friction is $$0.2$$, what is the acceleration of the block? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$5.6\ \mathrm{m/s^2$}$$

Question 12

A 5 kg block is at rest on a horizontal surface. The maximum static friction force before it starts to move is $$20\ \mathrm{N}. $$What is the coefficient of static friction?

Accepted Answer

$$0.41$$

Question 13

A 1.5 kg book rests on a table. What is the reaction force to the weight of the book?

Accepted Answer

The normal force exerted by the table on the book

Question 14

A 2 kg block is connected by a light string to a 3 kg block over a frictionless pulley. The 2 kg block is on a frictionless table, and the 3 kg block hangs off the edge. What is the acceleration of the system? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$5.88\ \mathrm{m/s^2$}$$

Question 15

A stubborn cow weighing $$1500\ \mathrm{N} is $$being pulled so that it slides at constant velocity. If the force required is $$391.6\ \mathrm{N}$$, what is the coefficient of kinetic friction?

Accepted Answer

$$0.26$$

Question 16

A block is on the verge of slipping down an incline. If the angle of the incline is $$	heta$$ and the coefficient of static friction is $$\mu_s$$, what is the minimum angle $$	heta_{min}$$ for slipping to occur?

Accepted Answer

$$	heta_{min} = \arctan(\mu_s)$$

Question 17

Which of the following best describes the purpose of a free-body diagram?

Accepted Answer

To represent all the forces acting on a single object

Question 18

A 50 kg person stands on a scale in an elevator accelerating upward at $$2\ \mathrm{m/s^2$}. $$What does the scale read? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$590\ \mathrm{N}$$

Dynamics: Newton's Laws of Motion – Study Notes (Giancoli, Chapter 4)

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