Q: A 10 kg object is pulled with a net force of 30 N. What is its acceleration?

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

Q: A skydiver of mass 80 kg descends at a steady speed. What is the magnitude of the upward force of air resistance acting on the skydiver?

$$F = mg = 80 \times 9.8 = 784\ \mathrm{N}$$

Q: A 2 kg object is suspended from a rope and is at rest. What is the tension in the rope?

$$T = mg = 2 \times 9.8 = 19.6\ \mathrm{N}$$

Q: A 3 kg object is being lowered with a downward acceleration of $$2.0\ \mathrm{m/s^2$}. $$What is the tension in the rope holding the object?

$$T = m(g - a) = 3 \times (9.8 - 2.0) = 3 \times 7.8 = 23.4\ \mathrm{N}$$

Question 1

Which of the following 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 5 kg box is at rest on a horizontal surface. According to Newton's First Law, what must be true about the forces acting on the box?

Accepted Answer

The net force acting on the box is zero.

Question 3

A 10 kg object is pulled with a net force of 30 N. What is its acceleration?

Accepted Answer

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

Question 4

Which of the following is NOT a property of force?

Accepted Answer

Force is a scalar quantity.

Question 5

A skydiver of mass 80 kg descends at a steady speed. What is the magnitude of the upward force of air resistance acting on the skydiver?

Accepted Answer

$$F = mg = 80 	imes 9.8 = 784\ \mathrm{N}$$

Question 6

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

Accepted Answer

Action and reaction forces act on different objects and are equal in magnitude but opposite in direction.

Question 7

A person pushes a wall with a force of 50 N. According to Newton's Third Law, what force does the wall exert on the person?

Accepted Answer

50 N in the opposite direction.

Question 8

A 2 kg object is suspended from a rope and is at rest. What is the tension in the rope?

Accepted Answer

$$T = mg = 2 	imes 9.8 = 19.6\ \mathrm{N}$$

Question 9

Which force is responsible for keeping a book at rest on a table?

Accepted Answer

The normal force exerted by the table.

Question 10

A crate is being pulled to the right with a force of 100 N, but does not move. What is the magnitude and direction of the friction force acting on the crate?

Accepted Answer

100 N to the left.

Question 11

A 3 kg object is being lowered with a downward acceleration of $$2.0\ \mathrm{m/s^2$}. $$What is the tension in the rope holding the object?

Accepted Answer

$$T = m(g - a) = 3 	imes (9.8 - 2.0) = 3 	imes 7.8 = 23.4\ \mathrm{N}$$

Question 12

Which of the following best describes the direction of the weight vector for an object near Earth's surface?

Accepted Answer

Directly downward, toward the center of the Earth.

Question 13

A 4 kg block is pulled horizontally with a net force of 20 N. What is its acceleration?

Accepted Answer

$$a = \frac{F_{	ext{net}}}{m} = \frac{20}{4} = 5\ \mathrm{m/s^2$}$$

Question 14

Which of the following is an example of a contact force?

Accepted Answer

Friction force between a crate and the floor.

Question 15

A car of mass 1000 kg accelerates from rest to $$10\ \mathrm{m/s} in 5 $$seconds. What is the net force acting on the car?

Accepted Answer

$$a = \frac{\Delta v}{\Delta t} = \frac{10}{5} = 2\ \mathrm{m/s^2$}$$, $$F_{	ext{net}} = ma = 1000 	imes 2 = 2000\ \mathrm{N}$$

Question 16

Which statement about the normal force is correct?

Accepted Answer

It acts perpendicular to the surface in contact.

Question 17

A 0.5 kg ball is thrown straight up. At the highest point, what is the net force acting on the ball (neglecting air resistance)?

Accepted Answer

$$F_{	ext{net}} = mg = 0.5 	imes 9.8 = 4.9\ \mathrm{N}$$\ downward

Question 18

A sled is pulled by a rope at an angle. Which force is responsible for the sled moving forward?

Accepted Answer

The tension force in the rope.

Question 19

A 60 kg person stands on a scale in an elevator accelerating upward at $$2\ \mathrm{m/s^2$}. $$What does the scale read?

Accepted Answer

$$N = m(g + a) = 60 	imes (9.8 + 2) = 60 	imes 11.8 = 708\ \mathrm{N}$$

Forces and Newton's Laws of Motion: Study Notes

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드