Q: A 10 kg box rests on a horizontal surface. If the coefficient of static friction between the box and the surface is 0.4, what is the maximum horizontal force that can be applied before the box starts to move? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

$$F_{max} = 0.4 \times 10 \times 9.8 = 39.2\ \mathrm{N}$$

Q: A 2 kg object is accelerating at $$3\ \mathrm{m/s^2$}. $$What is the net force acting on it?

$$F = 2 \times 3 = 6\ \mathrm{N}$$

Question 1

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

Accepted Answer

A body acted on by no net force moves with constant velocity and zero acceleration.

Question 2

A 10 kg box rests on a horizontal surface. If the coefficient of static friction between the box and the surface is 0.4, what is the maximum horizontal force that can be applied before the box starts to move? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$F_{max} = 0.4 	imes 10 	imes 9.8 = 39.2\ \mathrm{N}$$

Question 3

A car suddenly stops and the passengers lurch forward. Which property of matter is responsible for this effect?

Accepted Answer

Inertia

Question 4

A block of mass $$m is $$placed on an inclined plane of angle $$\alpha as $$shown. What is the expression for the normal force $$N$$ acting on the block?

Accepted Answer

$$N = mg \cos \alpha$$

Question 5

Which of the following is NOT a contact force?

Accepted Answer

Weight

Question 6

A 5 kg object is acted upon by two forces: $$\vec{F}_1 = 10\ \mathrm{N}$$ east and $$\vec{F}_2 = 6\ \mathrm{N}$$ north. What is the magnitude of the net force?

Accepted Answer

$$\sqrt{10^2$ + 6^2$} = 11.66\ \mathrm{N}$$

Question 7

A block is pulled by a rope with a force $$F at an $$angle $$	heta$$ above the horizontal. What is the horizontal component of the force?

Accepted Answer

$$F \cos 	heta$$

Question 8

A 2 kg object is accelerating at $$3\ \mathrm{m/s^2$}. $$What is the net force acting on it?

Accepted Answer

$$F = 2 	imes 3 = 6\ \mathrm{N}$$

Question 9

Which of the following best describes the direction of the friction force?

Accepted Answer

It acts parallel to the surface and opposes relative motion.

Question 10

A block of mass $$m is $$suspended by a rope. What is the tension $$T in $$the rope if the block is at rest?

Accepted Answer

$$T = mg$$

Question 11

A 4 kg and an 8 kg block are connected by a string and slide down a 30-degree incline. If the coefficient of kinetic friction for the 4 kg block is 0.25 and for the 8 kg block is 0.35, which block experiences a greater frictional force?

Accepted Answer

The 8 kg block, because friction depends on both mass and coefficient.

Question 12

Which equation correctly represents Newton's Second Law of Motion?

Accepted Answer

$$\sum \vec{F} = m\vec{a}$$

Question 13

A block is at rest on a horizontal surface. Which of the following statements is true?

Accepted Answer

The net force on the block is zero.

Question 14

A person pushes a box across a floor at constant speed. Which statement is correct?

Accepted Answer

The applied force is equal to the friction force.

Question 15

Which of the following is an example of a long-range force?

Accepted Answer

Weight (gravity)

Question 16

A block is pulled by two forces, $$\vec{F}_1$$ and $$\vec{F}_2$$, at a point. According to the superposition principle, what is the net effect?

Accepted Answer

The block experiences a force equal to the vector sum of $$\vec{F}_1$$ and $$\vec{F}_2.$$

Question 17

A 5 kg block is pulled with a force of 20 N on a frictionless surface. What is its acceleration?

Accepted Answer

$$a = 20 / 5 = 4\ \mathrm{m/s^2$}$$

Question 18

A block is sliding down an incline. Which force is responsible for its acceleration down the slope?

Accepted Answer

The component of gravity parallel to the incline

Question 19

A block is at rest on an inclined plane. Which of the following statements is true if the block does not slide?

Accepted Answer

The static friction force is equal to the component of gravity parallel to the incline.

Newton’s Laws of Motion: Forces, Equilibrium, and Dynamics

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