Q: A 1200 kg car is at rest. What net force is required to accelerate it at $$2.0\ \mathrm{m/s^2$}$$?

$$F = 1200\ \mathrm{kg} \times 2.0\ \mathrm{m/s^2$} = 2400\ \mathrm{N}$$

Q: A 55 kg sled is accelerated at $$1.4\ \mathrm{m/s^2$} on $$frictionless ice. What force is required?

$$F = 55\ \mathrm{kg} \times 1.4\ \mathrm{m/s^2$} = 77\ \mathrm{N}$$

Q: A 70 kg astronaut is floating in space. If she pushes a 10 kg tool away from her at $$2\ \mathrm{m/s}$$, what is her recoil velocity?

$$v = -\frac{10\ \mathrm{kg} \times 2\ \mathrm{m/s}}{70\ \mathrm{kg}} = -0.29\ \mathrm{m/s}$$

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 1200 kg car is at rest. What net force is required to accelerate it at $$2.0\ \mathrm{m/s^2$}$$?

Accepted Answer

$$F = 1200\ \mathrm{kg} 	imes 2.0\ \mathrm{m/s^2$} = 2400\ \mathrm{N}$$

Question 3

Which of the following statements about mass and weight is correct?

Accepted Answer

Mass is a measure of inertia and does not change with location, while weight is the force of gravity acting on an object and depends on the local gravitational acceleration.

Question 4

A 55 kg sled is accelerated at $$1.4\ \mathrm{m/s^2$} on $$frictionless ice. What force is required?

Accepted Answer

$$F = 55\ \mathrm{kg} 	imes 1.4\ \mathrm{m/s^2$} = 77\ \mathrm{N}$$

Question 5

Two people push a 1850 kg car with forces of 275 N and 395 N. If frictional forces total 560 N, what is the acceleration of the car?

Accepted Answer

$$a = \frac{275\ \mathrm{N} + 395\ \mathrm{N} - 560\ \mathrm{N}}{1850\ \mathrm{kg}} = \frac{110\ \mathrm{N}}{1850\ \mathrm{kg}} = 0.059\ \mathrm{m/s^2$}$$

Question 6

Which of the following is NOT an example of Newton's Third Law?

Accepted Answer

A ball rolling on a frictionless surface continues moving at constant velocity.

Question 7

A 70 kg astronaut is floating in space. If she pushes a 10 kg tool away from her at $$2\ \mathrm{m/s}$$, what is her recoil velocity?

Accepted Answer

$$v = -\frac{10\ \mathrm{kg} 	imes 2\ \mathrm{m/s}}{70\ \mathrm{kg}} = -0.29\ \mathrm{m/s}$$

Question 8

A box weighing 700 N rests on a table. A rope tied to the box runs vertically upward over a pulley, and a 600 N weight hangs from the other end. What is the normal force exerted by the table on the box?

Accepted Answer

$$F_N = 700\ \mathrm{N} - 600\ \mathrm{N} = 100\ \mathrm{N}$$

Question 9

Arlene, mass 50.0 kg, stands at the center of a high wire that sags at an angle of $$10.0^\circ$$ below the horizontal. What is the tension in the wire?

Accepted Answer

$$T = \frac{mg}{2 \sin 10.0^\circ} = \frac{50.0\ \mathrm{kg} 	imes 9.8\ \mathrm{m/s^2$}}{2 \sin 10.0^\circ} \approx 1420\ \mathrm{N}$$

Question 10

Which of the following is a correct statement about inertial reference frames?

Accepted Answer

An inertial reference frame is one in which Newton's first law holds true.

Question 11

A 10 kg box is pulled horizontally with a force of 50 N. If friction is 20 N, what is the acceleration of the box?

Accepted Answer

$$a = \frac{50\ \mathrm{N} - 20\ \mathrm{N}}{10\ \mathrm{kg}} = 3.0\ \mathrm{m/s^2$}$$

Question 12

A 5 kg object is acted on by two forces: 8 N to the right and 3 N to the left. What is the acceleration?

Accepted Answer

$$a = \frac{8\ \mathrm{N} - 3\ \mathrm{N}}{5\ \mathrm{kg}} = 1.0\ \mathrm{m/s^2$}$$

Question 13

Which of the following best explains why astronauts feel 'weightless' while orbiting Earth?

Accepted Answer

They are in free fall, accelerating toward Earth at the same rate as their spacecraft.

Question 14

A 20 kg box is suspended by a rope. What is the tension in the rope if the box is at rest?

Accepted Answer

$$T = mg = 20\ \mathrm{kg} 	imes 9.8\ \mathrm{m/s^2$} = 196\ \mathrm{N}$$

Question 15

A 10 kg object is dropped on the Moon, where $$g_{moon} = 1.6\ \mathrm{m/s^2$}. $$What is its weight on the Moon?

Accepted Answer

$$W = mg = 10\ \mathrm{kg} 	imes 1.6\ \mathrm{m/s^2$} = 16\ \mathrm{N}$$

Question 16

Which of the following is the correct SI unit for force?

Accepted Answer

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

Dynamics: Newton’s Laws of Motion (Chapter 4 Study Notes)

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