Question 1

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 2

A 10 kg box rests on a horizontal surface. If the coefficient of friction is negligible and a horizontal force of 20 N is applied, what is the acceleration of the box?

Accepted Answer

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

Question 3

Which of the following is NOT a contact force?

Accepted Answer

Weight

Question 4

A person pushes a box across a floor at constant velocity. Which statement is true about the forces acting on the box?

Accepted Answer

The net force on the box is zero.

Question 5

A 5 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

$$49\ \mathrm{N}$$

Question 6

Which of the following best describes an inertial frame of reference?

Accepted Answer

A frame of reference in which Newton's first law is valid.

Question 7

A car of mass $$m is $$moving in a circle of radius $$r at $$constant speed $$v. $$What is the direction of the net force acting on the car?

Accepted Answer

Toward the center of the circle

Question 8

If the net external force on an object is doubled while its mass remains constant, what happens to its acceleration?

Accepted Answer

It doubles.

Question 9

A 2 kg object and a 4 kg object are both acted on by the same net external force. How do their accelerations compare?

Accepted Answer

The 2 kg object has twice the acceleration of the 4 kg object.

Question 10

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

Accepted Answer

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

Question 11

A 3 kg object is acted on by a net force of $$12\ \mathrm{N}. $$What is its acceleration?

Accepted Answer

$$4\ \mathrm{m/s^2$}$$

Question 12

Which of the following is a correct statement of Newton's Third Law?

Accepted Answer

For every action, there is an equal and opposite reaction.

Question 13

A person stands on a scale in an elevator accelerating upward. How does the normal force (scale reading) compare to the person's weight?

Accepted Answer

The normal force is greater than the weight.

Question 14

Which of the following is the correct SI unit for force?

Accepted Answer

Newton (N)

Question 15

A block is pulled by a rope at an angle of $$30^\circ$$ above the horizontal with a force of $$10\ \mathrm{N}. $$What is the horizontal component of the force?

Accepted Answer

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

Question 16

A 70 kg astronaut weighs less on the Moon than on Earth. Which of the following best explains why?

Accepted Answer

The acceleration due to gravity $$g is $$less on the Moon.

Question 17

A box is at rest on a horizontal surface. Which force is responsible for supporting the box against gravity?

Accepted Answer

The normal force

Question 18

A runner pushes backward on the ground to start running. According to Newton's Third Law, what is the reaction force?

Accepted Answer

The ground pushes forward on the runner's foot.

Question 19

A 2 kg object is acted on by two forces: $$\vec{F}_1 = 3\ \mathrm{N} to $$the right and $$\vec{F}_2 = 4\ \mathrm{N}$$ upward. What is the magnitude of the object's acceleration?

Accepted Answer

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

Question 20

Which of the following best describes the superposition principle for forces?

Accepted Answer

The net force on an object is the vector sum of all individual forces acting on it.

Newton's Laws of Motion: Foundations of Dynamics

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