Question 1

A 5 kg box rests on a horizontal surface. If the coefficient of friction between the box and the surface is 0.2, what is the minimum horizontal force required to start moving the box? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$F = 9.8\ \mathrm{N}$$

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 10 N force is applied at an angle of $$30^\circ$$ above the horizontal to a box on a frictionless surface. What is the horizontal component of the force?

Accepted Answer

$$10 \cos 30^\circ = 8.66\ \mathrm{N}$$

Question 4

A 2 kg object is acted on by a net force of $$6\ \mathrm{N} to $$the right. What is its acceleration?

Accepted Answer

$$a = 3\ \mathrm{m/s^2$}$$

Question 5

A 70 kg astronaut weighs less on the Moon than on Earth. Which of the following quantities is different on the Moon compared to Earth?

Accepted Answer

The astronaut's weight

Question 6

A car accelerates forward because the ground pushes on the tires. Which law explains this phenomenon?

Accepted Answer

Newton's Third Law

Question 7

A block is at rest on an inclined plane. Which force is responsible for preventing the block from sliding down?

Accepted Answer

Friction force

Question 8

If the net force on an object is zero, which of the following must be true?

Accepted Answer

The object is in equilibrium.

Question 9

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

Accepted Answer

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

Question 10

A hockey puck slides on frictionless ice and is struck by a stick, giving it a force to the right. What happens to the puck after the stick is no longer in contact?

Accepted Answer

It moves with constant velocity to the right.

Question 11

A 4 kg object is acted on by two forces: $$\vec{F}_1 = 6\ \mathrm{N}$$ east and $$\vec{F}_2 = 8\ \mathrm{N}$$ north. What is the magnitude of the object's acceleration?

Accepted Answer

$$a = 2.5\ \mathrm{m/s^2$}$$

Question 12

Which of the following is NOT a contact force?

Accepted Answer

Weight

Question 13

A runner pushes backward on the ground with her foot. According to Newton's third law, what is the reaction force?

Accepted Answer

The ground pushes forward on her foot.

Question 14

A 10 kg box is pulled with a force of $$50\ \mathrm{N} at an $$angle of $$60^\circ$$ above the horizontal. What is the vertical component of the force?

Accepted Answer

$$50 \sin 60^\circ = 43.3\ \mathrm{N}$$

Question 15

A 2 kg object is moving in a circle of radius 3 m at constant speed. If the net force is always directed toward the center, what is this force called?

Accepted Answer

Centripetal force

Question 16

A person in an accelerating bus feels pushed backward. Why does this happen?

Accepted Answer

The person is in a non-inertial frame of reference.

Question 17

Which equation correctly expresses Newton's Second Law?

Accepted Answer

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

Question 18

A 5 kg object is acted on by a net force of $$20\ \mathrm{N}. If $$the same force is applied to a 10 kg object, what is the acceleration?

Accepted Answer

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

Question 19

A block is pulled by two forces: $$\vec{F}_1 = 10\ \mathrm{N}$$ east and $$\vec{F}_2 = 10\ \mathrm{N}$$ west. What is the net force on the block?

Accepted Answer

$$0\ \mathrm{N}$$

Question 20

A 1 kg object is dropped from rest. What is the magnitude of the gravitational force acting on it near Earth's surface?

Accepted Answer

$$9.8\ \mathrm{N}$$

Ch 4: Newton’s Laws of Motion

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