Q: A rocket sled of mass 2100 kg is accelerated by four rockets. The initial acceleration is $$a = 49\ \mathrm{m/s^2$}$$ and the friction force is $$650\ \mathrm{N}. $$What is the thrust $$T$$ produced by each rocket?

$$T = \frac{(2100 \times 49) + 650}{4} = 25,787.5\ \mathrm{N}$$

Q: A skier of mass $$60.0\ \mathrm{kg} is on a $$slope. If friction is ignored, what is her acceleration down the slope if the angle of the slope is $$30^\circ$$?

$$a = g \sin 30^\circ = 9.8 \times 0.5 = 4.9\ \mathrm{m/s^2$}$$

Q: A 75 kg orangutan hangs from two arms, each making a $$30^\circ$$ angle with the horizontal. What is the tension in each arm?

$$T = \frac{mg}{2 \sin 30^\circ} = \frac{75 \times 9.8}{2 \times 0.5} = 735\ \mathrm{N}$$

Q: A 75.0-kg man stands on a scale in an elevator accelerating upward at $$2.0\ \mathrm{m/s^2$}. $$What does the scale read?

$$F = m(g + a) = 75.0 \times (9.8 + 2.0) = 885\ \mathrm{N}$$

Q: A tugboat exerts a force of $$2.5 \times 10^3$\ \mathrm{N} in $$the x-direction and another exerts $$3.6 \times 10^3$\ \mathrm{N} in $$the y-direction on a barge of mass $$5.0 \times 10^3$\ \mathrm{kg}. If $$the acceleration is $$7.5 \times 10$$^{-1}$$\ \mathrm{m/s^2$}$$, what is the drag force of the water?

$$F_{\text{drag}} = \sqrt{(2.5 \times 10^3$)^2 + (3.6$$ \times $$10^3)^2$} - (5.0 \times 10^3$ \times 7.5 \times 10$$^{-1}$$) = 4,360 - 3,750 = 610\ \mathrm{N}$$

Question 1

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

Accepted Answer

An object at rest remains at rest, and an object in motion remains in motion at constant velocity unless acted upon by a net external force.

Question 2

A 24 kg lawn mower is pushed with a net external force of 13 N parallel to the ground. What is its acceleration?

Accepted Answer

$$a = \frac{13}{24} = 0.54\ \mathrm{m/s^2$}$$

Question 3

Which of the following is NOT a vector quantity?

Accepted Answer

Mass

Question 4

A rocket sled of mass 2100 kg is accelerated by four rockets. The initial acceleration is $$a = 49\ \mathrm{m/s^2$}$$ and the friction force is $$650\ \mathrm{N}. $$What is the thrust $$T$$ produced by each rocket?

Accepted Answer

$$T = \frac{(2100 	imes 49) + 650}{4} = 25,787.5\ \mathrm{N}$$

Question 5

Which of the following best describes the concept of inertia?

Accepted Answer

The property of a body to remain at rest or in uniform motion unless acted upon by a net external force.

Question 6

A skier of mass $$60.0\ \mathrm{kg} is on a $$slope. If friction is ignored, what is her acceleration down the slope if the angle of the slope is $$30^\circ$$?

Accepted Answer

$$a = g \sin 30^\circ = 9.8 	imes 0.5 = 4.9\ \mathrm{m/s^2$}$$

Question 7

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

Accepted Answer

$$F = m \cdot a$$

Question 8

A 75 kg orangutan hangs from two arms, each making a $$30^\circ$$ angle with the horizontal. What is the tension in each arm?

Accepted Answer

$$T = \frac{mg}{2 \sin 30^\circ} = \frac{75 	imes 9.8}{2 	imes 0.5} = 735\ \mathrm{N}$$

Question 9

A 75.0-kg man stands on a scale in an elevator accelerating upward at $$2.0\ \mathrm{m/s^2$}. $$What does the scale read?

Accepted Answer

$$F = m(g + a) = 75.0 	imes (9.8 + 2.0) = 885\ \mathrm{N}$$

Question 10

Which of the following statements about free-body diagrams is correct?

Accepted Answer

They illustrate all the external forces acting on a body or system of interest.

Question 11

A tugboat exerts a force of $$2.5 	imes 10^3$\ \mathrm{N} in $$the x-direction and another exerts $$3.6 	imes 10^3$\ \mathrm{N} in $$the y-direction on a barge of mass $$5.0 	imes 10^3$\ \mathrm{kg}. If $$the acceleration is $$7.5 	imes 10$$^{-1}$$\ \mathrm{m/s^2$}$$, what is the drag force of the water?

Accepted Answer

$$F_{	ext{drag}} = \sqrt{(2.5 	imes 10^3$)^2 + (3.6$$ 	imes $$10^3)^2$} - (5.0 	imes 10^3$ 	imes 7.5 	imes 10$$^{-1}$$) = 4,360 - 3,750 = 610\ \mathrm{N}$$

Question 12

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

Accepted Answer

When you push on a wall, the wall pushes back on you with an equal and opposite force.

Question 13

A book of mass $$2.18\ \mathrm{kg} is $$pushed with a force of $$1.22\ \mathrm{N} on a $$frictionless surface. What force does the book exert back according to Newton's Third Law?

Accepted Answer

$$1.22\ \mathrm{N} in $$the opposite direction

Question 14

A tightrope walker of mass $$70.0\ \mathrm{kg} is $$supported by a wire. What is the tension in the wire?

Accepted Answer

$$T = mg = 70.0 	imes 9.8 = 686\ \mathrm{N}$$

Question 15

Which of the following best describes the difference between mass and weight?

Accepted Answer

Mass is the amount of matter in an object; weight is the force due to gravity acting on that mass.

Question 16

A soccer player starts from rest and accelerates forward, reaching a speed of $$6.0\ \mathrm{m/s} in$$ $$12.5\ \mathrm{s}. $$What was his average acceleration?

Accepted Answer

$$a = \frac{\Delta v}{\Delta t} = \frac{6.0}{12.5} = 0.48\ \mathrm{m/s^2$}$$

Question 17

If the only force acting on an object is gravity, what is the net force on the object?

Accepted Answer

$$F_{	ext{net}} = mg$$

Dynamics: Newton's Laws of Motion – Study Notes

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