Q: If the book is at rest on the table and not accelerating, what can you conclude about the net force acting on the book?

The net force is zero: $$\vec{F}_{\text{net}} = 0$$

Q: A tug-of-war team pulls on a rope with a force $$F_1 to $$the right, while the opposing team pulls with a force $$F_2 to $$the left. What is the net force on the rope if $$F_1 = 800$$\ \mathrm{N}$$ and F_2$ = 750\ \mathrm{N}$$?

$$F_{\text{net}} = 50\ \mathrm{N} to $$the right

Q: A 5 kg box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is $$\mu_s = 0.4. $$What is the maximum static friction force that can act on the box?

$$f_s$$^{\text{max}$$} = 19.6\ \mathrm{N}$$

Q: Which equation correctly represents the relationship between the net force and acceleration for an object of mass $$m$$?

$$\vec{a} = \frac{\vec{F}_{\text{net}}}{m}$$

Question 1

A book of mass $$m$$ rests on a table. What is the magnitude of the normal force $$N$$ exerted by the table on the book, assuming the table is horizontal and there are no other vertical forces acting?

Accepted Answer

$$N = m g$$

Question 2

If the book is at rest on the table and not accelerating, what can you conclude about the net force acting on the book?

Accepted Answer

The net force is zero: $$\vec{F}_{	ext{net}} = 0$$

Question 3

A tug-of-war team pulls on a rope with a force $$F_1 to $$the right, while the opposing team pulls with a force $$F_2 to $$the left. What is the net force on the rope if $$F_1 = 800$$\ \mathrm{N}$$ and F_2$ = 750\ \mathrm{N}$$?

Accepted Answer

$$F_{	ext{net}} = 50\ \mathrm{N} to $$the right

Question 4

A 2 kg book is placed on a table. What is the weight of the book?

Accepted Answer

$$w = 19.6\ \mathrm{N}$$

Question 5

If the table is suddenly removed from under the book, what is the net force on the book in the vertical ($$y) $$direction immediately after?

Accepted Answer

$$F_{	ext{net},y} = -m g$$

Question 6

A box is pushed across a rough floor and then released. What happens to the box after it is released?

Accepted Answer

The box will eventually come to a stop due to friction.

Question 7

Which of the following best describes the direction of the normal force exerted by a table on a book resting on it?

Accepted Answer

Perpendicular to the surface of the table, pointing upward.

Question 8

A 5 kg box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is $$\mu_s = 0.4. $$What is the maximum static friction force that can act on the box?

Accepted Answer

$$f_s$$^{	ext{max}$$} = 19.6\ \mathrm{N}$$

Question 9

Which equation correctly represents the relationship between the net force and acceleration for an object of mass $$m$$?

Accepted Answer

$$\vec{a} = \frac{\vec{F}_{	ext{net}}}{m}$$

Question 10

A box of mass $$m is $$sliding on a horizontal surface with a coefficient of kinetic friction $$\mu_k. $$What is the magnitude of the kinetic friction force acting on the box?

Accepted Answer

$$f_k = \mu_k N$$

Question 11

A 10 kg crate is at rest on a horizontal floor. If the coefficient of static friction is $$\mu_s = 0.5$$, what is the minimum horizontal force required to start moving the crate?

Accepted Answer

$$F = 49\ \mathrm{N}$$

Question 12

If a box is moving at constant velocity across a rough surface, what can you say about the net force acting on it?

Accepted Answer

The net force is zero.

Question 13

A 3 kg book is placed on a table. What is the normal force exerted by the table if the book is at rest and the table is horizontal?

Accepted Answer

$$N = 29.4\ \mathrm{N}$$

Question 14

A box is sliding to the right on a horizontal surface. Which direction does the friction force act?

Accepted Answer

To the left, opposite to the direction of motion.

Question 15

Which of the following statements about friction is correct?

Accepted Answer

Static friction can vary up to a maximum value, while kinetic friction is constant for a given normal force.

Question 16

A 4 kg box is pushed with a force of 20 N across a horizontal surface. The coefficient of kinetic friction is $$\mu_k = 0.3. $$What is the acceleration of the box?

Accepted Answer

$$a = 2.525\ \mathrm{m/s^2$}$$

Question 17

Which of the following best explains why a box sliding on a floor eventually comes to a stop?

Accepted Answer

Friction exerts a force in the opposite direction to the motion of the box.

Question 18

A 6 kg object is at rest on a horizontal table. If the table is replaced with one that is more easily deformed (softer), what happens to the normal force?

Accepted Answer

The normal force remains $$N = m g as $$long as the object is at rest and the table supports it.

Question 19

A 2 kg block is at rest on a table. If a downward force of 10 N is applied on top of the block, what is the new normal force exerted by the table?

Accepted Answer

$$N = 29.6\ \mathrm{N}$$

Forces and Newton's Laws: Normal Force, Gravity, and Friction

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