Q: A jet with a mass of $$51,000\ \mathrm{kg}$$ accelerates from rest to $$70\ \mathrm{m/s}$$ over a distance of $$940\ \mathrm{m}. $$What is the magnitude of the acceleration?

$$a = \frac{(70)^2$}{2 \times 940} = 2.61\ \mathrm{m/s^2$}$$

Q: A rope pulls a sled with a tension of $$50\ \mathrm{N} at an $$angle of $$30^\circ$$ above the horizontal. What is the horizontal component of the tension?

$$T_x = 50 \times \cos 30^\circ = 43.3\ \mathrm{N}$$

Question 1

A hockey puck slides across a frictionless ice surface. According to Newton's First Law, what will happen to the puck if no forces act on it?

Accepted Answer

It will continue moving in a straight line at constant speed.

Question 2

Which of the following best describes the direction of the weight force acting on an object near Earth's surface?

Accepted Answer

Vertically downward toward the center of the Earth.

Question 3

A 2 kg block is pulled across a horizontal surface by a constant force of 10 N. If the frictional force is 2 N, what is the acceleration of the block?

Accepted Answer

$$a = \frac{10 - 2}{2} = 4\ \mathrm{m/s^2$}$$

Question 4

Which of the following is NOT a contact force?

Accepted Answer

Weight (gravitational force)

Question 5

A jet with a mass of $$51,000\ \mathrm{kg}$$ accelerates from rest to $$70\ \mathrm{m/s}$$ over a distance of $$940\ \mathrm{m}. $$What is the magnitude of the acceleration?

Accepted Answer

$$a = \frac{(70)^2$}{2 	imes 940} = 2.61\ \mathrm{m/s^2$}$$

Question 6

If the net force on an object is zero, which statement is true about its motion?

Accepted Answer

It could be moving at constant velocity.

Question 7

A person pushes a box with a force of $$F to $$the right, and the box pushes back with a force of $$-F to $$the left. Which law does this illustrate?

Accepted Answer

Newton's Third Law

Question 8

Which of the following is the correct vector equation for the net force acting on an object?

Accepted Answer

$$\vec{F}_{\mathrm{net}} = \vec{F}_1 + \vec{F}_2 + \vec{F}_3 + \ldots$$

Question 9

A car crashes into a wall and comes to a stop, but the dummy inside continues moving forward until it hits the dashboard. This scenario best demonstrates:

Accepted Answer

Newton's First Law (Law of Inertia)

Question 10

A compressed spring exerts a force on a block. What type of force is this?

Accepted Answer

Spring force

Question 11

A rocket accelerates upward by expelling hot gases downward. What is the action-reaction pair in this scenario?

Accepted Answer

The rocket pushes the gases downward, and the gases push the rocket upward.

Question 12

Which force is responsible for keeping a person from slipping while walking?

Accepted Answer

Static friction

Question 13

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

Accepted Answer

It is halved.

Question 14

A box is at rest on a table. Which force balances the weight of the box?

Accepted Answer

Normal force

Question 15

A rope pulls a sled with a tension of $$50\ \mathrm{N} at an $$angle of $$30^\circ$$ above the horizontal. What is the horizontal component of the tension?

Accepted Answer

$$T_x = 50 	imes \cos 30^\circ = 43.3\ \mathrm{N}$$

Question 16

Which of the following statements about Newton's Third Law is correct?

Accepted Answer

Action and reaction forces are equal in magnitude and opposite in direction.

Question 17

A block slides across a rough surface and slows down. Which force is responsible for this change in motion?

Accepted Answer

Kinetic friction

Question 18

A $$10\ \mathrm{kg}$$ object is acted upon by a net force of $$30\ \mathrm{N}. $$What is its acceleration?

Accepted Answer

$$a = \frac{30}{10} = 3\ \mathrm{m/s^2$}$$

Question 19

Which of the following is the SI unit of force?

Accepted Answer

Newton ($$\mathrm{N})$$

Question 20

A block is pulled by two forces: $$F_1 = 8$$\ \mathrm{N}$$ to the right and F_2$ = 5\ \mathrm{N} to $$the left. What is the net force acting on the block?

Accepted Answer

$$F_{\mathrm{net}} = 8 - 5 = 3\ \mathrm{N}$$

Forces and Newton’s Laws of Motion – Study Notes

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