Q: A 5 kg box rests on a horizontal surface. What is the normal force acting on the box? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

$$N = mg = 5 \times 9.8 = 49\ \mathrm{N}$$

Q: A person stands on a scale in an elevator accelerating upward at $$2\ \mathrm{m/s^2$}. If $$the person's mass is 60 kg, what does the scale read?

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

Q: A sled of mass 4 kg is pulled by two ropes, each with a tension of 55 N at $$35^\circ$$ above the horizontal, as shown in the image. What is the total horizontal force on the sled?

$$F_{\text{horizontal}} = 2 \times 55 \times \cos 35^\circ = 90.2\ \mathrm{N}$$

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 2 kg block is acted on by a net force of 10 N. What is its acceleration?

Accepted Answer

$$a = \frac{F}{m} = \frac{10}{2} = 5\ \mathrm{m/s^2$}$$

Question 3

Which of the following is NOT a correct statement about mass?

Accepted Answer

Mass is a vector quantity.

Question 4

A 70 kg astronaut pushes on a satellite with a force of 100 N. According to Newton's Third Law, what force does the satellite exert on the astronaut?

Accepted Answer

100 N in the opposite direction

Question 5

A 5 kg box rests on a horizontal surface. What is the normal force acting on the box? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$N = mg = 5 	imes 9.8 = 49\ \mathrm{N}$$

Question 6

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

Accepted Answer

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

Question 7

Which of the following is a correct free-body diagram for a book resting on a table?

Accepted Answer

Two forces: weight downward and normal force upward, equal in magnitude.

Question 8

A sled of mass 4 kg is pulled by two ropes, each with a tension of 55 N at $$35^\circ$$ above the horizontal, as shown in the image. What is the total horizontal force on the sled?

Accepted Answer

$$F_{	ext{horizontal}} = 2 	imes 55 	imes \cos 35^\circ = 90.2\ \mathrm{N}$$

Question 9

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

Accepted Answer

The object's velocity is constant.

Question 10

A 10 kg box is pushed across a frictionless surface with a force of 40 N. What is the acceleration of the box?

Accepted Answer

$$a = \frac{F}{m} = \frac{40}{10} = 4\ \mathrm{m/s^2$}$$

Question 11

Which of the following statements about the normal force is correct?

Accepted Answer

The normal force is always perpendicular to the surface.

Question 12

A 3 kg object is acted on by two forces: $$F_1 = 6$$\ \mathrm{N}$$ to the right and F_2$ = 4\ \mathrm{N} to $$the left. What is the acceleration of the object?

Accepted Answer

$$a = \frac{6 - 4}{3} = 0.67\ \mathrm{m/s^2$}$$\ 	ext{to the right}

Question 13

Which of the following is an example of an action-reaction pair according to Newton's Third Law?

Accepted Answer

A car pushes on the ground, and the ground pushes back on the car.

Question 14

A 0.145 kg baseball is hit with a force of 700 N. What is the resulting acceleration?

Accepted Answer

$$a = \frac{700}{0.145} = 4828\ \mathrm{m/s^2$}$$

Question 15

Which of the following best describes the concept of apparent weight?

Accepted Answer

The force felt from contact with a floor or scale, which may differ from actual weight if accelerating.

Question 16

A 1200 kg car is accelerated by a net force of 7000 N. What is the acceleration of the car?

Accepted Answer

$$a = \frac{7000}{1200} = 5.83\ \mathrm{m/s^2$}$$

Question 17

A 4 kg sled is pulled with a force of 6.20 N at $$35^\circ$$ above the horizontal. What is the horizontal component of the force?

Accepted Answer

$$F_x = 6.20 \cos 35^\circ = 5.08\ \mathrm{N}$$

Question 18

Which of the following is true about forces in two dimensions?

Accepted Answer

Each dimension can be treated separately when applying Newton's laws.

Newton’s Laws of Motion – Physics with Calculus Study Notes

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