Q: A 5.2-kg salmon is hanging from a fish scale attached to the ceiling of an elevator. If the elevator accelerates upward at $$3.5\ \mathrm{m/s^2$}$$, what is the apparent weight of the salmon?

$$W_{\text{apparent}} = m(g + a) = 5.2\ \mathrm{kg} \times (9.8\ \mathrm{m/s^2$} + 3.5\ \mathrm{m/s^2$}) = 68.64\ \mathrm{N}$$

Q: A jetliner with a mass of $$1.75 \times 10^5$\ \mathrm{kg}$$ and an initial speed of $$26.8\ \mathrm{m/s} is $$slowed to a stop by its brakes. If the net braking force is $$3.50 \times 10^5$\ \mathrm{N}$$, what is the acceleration of the jetliner?

$$a = \frac{F}{m} = \frac{3.50 \times 10^5$\ \mathrm{N}}{1.75 \times 10^5$\ \mathrm{kg}} = 2.0\ \mathrm{m/s^2$}$$

Q: A person pulls a sled with a force of $$F = 620\ \mathrm{N} at an $$angle of $$30^\circ$$ above the horizontal. What is the horizontal component of the force?

$$F_x = F \cos \theta = 620\ \mathrm{N} \cos 30^\circ = 537\ \mathrm{N}$$

Q: A $$3.0\ \mathrm{kg}$$ object is placed on a scale in an elevator accelerating downward at $$2.3\ \mathrm{m/s^2$}. $$What is the apparent weight shown on the scale?

$$W_{\text{apparent}} = m(g - a) = 3.0\ \mathrm{kg} \times (9.8 - 2.3)\ \mathrm{m/s^2$} = 22.5\ \mathrm{N}$$

Q: A $$5.0\ \mathrm{kg}$$ box is pulled by two ropes, each with a force of $$55\ \mathrm{N} at$$ $$35^\circ$$ above the horizontal in opposite directions. What is the total horizontal force on the box?

$$F_{\text{total}} = 2 \times 55\ \mathrm{N} \times \cos 35^\circ = 90.1\ \mathrm{N}$$

Question 1

A 5.2-kg salmon is hanging from a fish scale attached to the ceiling of an elevator. If the elevator accelerates upward at $$3.5\ \mathrm{m/s^2$}$$, what is the apparent weight of the salmon?

Accepted Answer

$$W_{	ext{apparent}} = m(g + a) = 5.2\ \mathrm{kg} 	imes (9.8\ \mathrm{m/s^2$} + 3.5\ \mathrm{m/s^2$}) = 68.64\ \mathrm{N}$$

Question 2

Which statement best describes Newton's First Law of Motion?

Accepted Answer

An object will remain at rest or move at a constant velocity unless acted upon by a net external force.

Question 3

A box of mass $$10.0\ \mathrm{kg}$$ rests on a smooth, horizontal floor in contact with a box of mass $$5.00\ \mathrm{kg}. If a $$horizontal force of $$30.0\ \mathrm{N} is $$applied to the $$10.0\ \mathrm{kg}$$ box, what is the acceleration of the system?

Accepted Answer

$$a = \frac{F}{m_1$ + m_2$} = \frac{30.0\ \mathrm{N}}{10.0\ \mathrm{kg} + 5.00\ \mathrm{kg}} = 2.0\ \mathrm{m/s^2$}$$

Question 4

A child of mass $$m$$ rides a toboggan down a frictionless, ice-covered hill inclined at an angle $$	heta$$ with respect to the horizontal. What is the acceleration of the child?

Accepted Answer

$$a = g \sin 	heta$$

Question 5

Two canoeists meet in the middle of a lake. A person in canoe 1 pushes on canoe 2 with a force of $$46\ \mathrm{N} to $$separate the canoes. The mass of canoe 1 and its occupants is $$150\ \mathrm{kg}$$, and the mass of canoe 2 and its occupants is $$250\ \mathrm{kg}. $$What is the acceleration of canoe 2?

Accepted Answer

$$a_2$$ = \frac{F}{$$m_2$$} = \frac{46\ \mathrm{N}}{250\ \mathrm{kg}} = 0.184\ \mathrm{$$m/s^2$$}$$

Question 6

Which of the following is NOT a property of force?

Accepted Answer

Force is a scalar quantity.

Question 7

A jetliner with a mass of $$1.75 	imes 10^5$\ \mathrm{kg}$$ and an initial speed of $$26.8\ \mathrm{m/s} is $$slowed to a stop by its brakes. If the net braking force is $$3.50 	imes 10^5$\ \mathrm{N}$$, what is the acceleration of the jetliner?

Accepted Answer

$$a = \frac{F}{m} = \frac{3.50 	imes 10^5$\ \mathrm{N}}{1.75 	imes 10^5$\ \mathrm{kg}} = 2.0\ \mathrm{m/s^2$}$$

Question 8

Which of the following best describes Newton's Third Law of Motion?

Accepted Answer

For every force exerted by object 1 on object 2, object 2 exerts an equal and opposite force on object 1.

Question 9

A person pulls a sled with a force of $$F = 620\ \mathrm{N} at an $$angle of $$30^\circ$$ above the horizontal. What is the horizontal component of the force?

Accepted Answer

$$F_x = F \cos 	heta = 620\ \mathrm{N} \cos 30^\circ = 537\ \mathrm{N}$$

Question 10

Which of the following statements about normal force is correct?

Accepted Answer

The normal force is always perpendicular to the surface.

Question 11

A $$3.0\ \mathrm{kg}$$ object is placed on a scale in an elevator accelerating downward at $$2.3\ \mathrm{m/s^2$}. $$What is the apparent weight shown on the scale?

Accepted Answer

$$W_{	ext{apparent}} = m(g - a) = 3.0\ \mathrm{kg} 	imes (9.8 - 2.3)\ \mathrm{m/s^2$} = 22.5\ \mathrm{N}$$

Question 12

Which of the following is a correct application of Newton's Second Law in vector form?

Accepted Answer

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

Question 13

A $$5.0\ \mathrm{kg}$$ box is pulled by two ropes, each with a force of $$55\ \mathrm{N} at$$ $$35^\circ$$ above the horizontal in opposite directions. What is the total horizontal force on the box?

Accepted Answer

$$F_{	ext{total}} = 2 	imes 55\ \mathrm{N} 	imes \cos 35^\circ = 90.1\ \mathrm{N}$$

Question 14

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

Accepted Answer

Apparent weight is the contact force felt from a scale or floor, which may differ from actual weight if the surroundings are accelerating.

Question 15

A $$2.0\ \mathrm{kg}$$ block is placed on a frictionless table. If a force of $$10.0\ \mathrm{N} is $$applied horizontally, what is the acceleration of the block?

Accepted Answer

$$a = \frac{F}{m} = \frac{10.0\ \mathrm{N}}{2.0\ \mathrm{kg}} = 5.0\ \mathrm{m/s^2$}$$

Question 16

Which of the following is true about the normal force acting on an object on an inclined plane?

Accepted Answer

The normal force is less than the object's weight and is given by $$N = mg \cos 	heta.$$

Question 17

Which of the following is a correct statement about action-reaction pairs?

Accepted Answer

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

Newton's Laws of Motion: Study Notes (Chapter 5)

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