Q: A 2 kg object is on Earth where $$g = 9.8\ \mathrm{m/s^2$}. $$What is its weight?

$$w = 2 \times 9.8 = 19.6\ \mathrm{N}$$

Question 1

A car of mass 1200 kg is at rest on a flat road. According to Newton's First Law, what will happen to the car if no net external force acts on it?

Accepted Answer

It will remain at rest.

Question 2

A rocket sled of mass 2100 kg experiences a net force of 6500 N. What is its acceleration? Use $$F = ma.$$

Accepted Answer

$$a = \frac{6500}{2100} = 3.10\ \mathrm{m/s^2$}$$

Question 3

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

Accepted Answer

For every action, there is an equal and opposite reaction acting on different objects.

Question 4

A person pulls a box with a rope on a frictionless surface. If the tension in the rope is 50 N and the box has a mass of 10 kg, what is the acceleration of the box? Use $$F = ma.$$

Accepted Answer

$$a = \frac{50}{10} = 5\ \mathrm{m/s^2$}$$

Question 5

Which statement about weight and mass is correct?

Accepted Answer

Weight is the gravitational force acting on a mass.

Question 6

A 2 kg object is on Earth where $$g = 9.8\ \mathrm{m/s^2$}. $$What is its weight?

Accepted Answer

$$w = 2 	imes 9.8 = 19.6\ \mathrm{N}$$

Question 7

In a free-body diagram of a book resting on a table, which forces should be shown?

Accepted Answer

Gravitational force downward and normal force upward.

Question 8

A lawnmower of mass 21 kg is pushed with a net force of 51 N. What is its acceleration? Use $$F = ma.$$

Accepted Answer

$$a = \frac{51}{21} = 2.43\ \mathrm{m/s^2$}$$

Question 9

A student claims that heavier objects fall faster than lighter ones. Which concept from Newton's Laws refutes this misconception?

Accepted Answer

Newton's Second Law: Acceleration is independent of mass when only gravity acts.

Question 10

A rope pulls two blocks connected in a straight line on a frictionless surface. If the tension in the rope is 30 N and each block has a mass of 5 kg, what is the acceleration of the system?

Accepted Answer

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

Question 11

Which of the following is true about tension in a massless, frictionless rope connecting two objects?

Accepted Answer

Tension acts away from the object in both directions.

Question 12

A rocket launches upward. According to Newton's Third Law, what is the reaction force to the rocket's exhaust gases pushing downward?

Accepted Answer

The exhaust gases push the rocket upward.

Question 13

A 5 kg object is suspended by a rope. What is the tension in the rope if the object is at rest? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

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

Question 14

Which scenario best illustrates Newton's First Law?

Accepted Answer

A ball rolling on a smooth surface continues moving until friction slows it down.

Question 15

A student draws a free-body diagram for a car accelerating forward. Which forces should be included?

Accepted Answer

Forward force from the engine, friction, gravity, and normal force.

Question 16

If a net force of zero acts on an object, what can be said about its motion?

Accepted Answer

It will move with constant velocity.

Question 17

A 3 kg object is dropped from rest. Ignoring air resistance, what is its acceleration as it falls?

Accepted Answer

$$a = 9.8\ \mathrm{m/s^2$}$$

Question 18

A person stands on a scale in an elevator accelerating upward at $$2\ \mathrm{m/s^2$}. If $$the person's mass is 70 kg, what is the apparent weight? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$w = 70 	imes (9.8 + 2) = 826\ \mathrm{N}$$

Question 19

Which of the following is a common misconception about Newton's Laws?

Accepted Answer

Heavier objects fall faster than lighter ones.

Chapter 4 Newton's Laws of Motion — Study Guide

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