Q: The Mars Rover Perseverance weighed about 10,000 N on Earth and 3,790 N on Mars. What is the gravitational acceleration on Mars?

$$g_{Mars} = 3.7\,\text{m/s}^2$$

Q: A bathroom scale measures your 'weight' as 70 kg. What is your real weight on Earth's surface?

$$W = 70 \times 9.8 = 686\,\text{N}$$

Question 1

Which of the following best describes a force according to Newton's laws?

Accepted Answer

A vector quantity that changes an object's velocity.

Question 2

A 10 kg block is pulled to the right by a force of 70 N and to the left by a force of 20 N. What is the acceleration of the block?

Accepted Answer

$$a = \frac{70 - 20}{10}$$

Question 3

When expanding $$\Sigma F = ma$$, how should the sign of the acceleration be interpreted?

Accepted Answer

It indicates the direction of the acceleration.

Question 4

A 10 kg box accelerates to the left at $$6\,	ext{m/s}^2$$, pushed by two forces. If the box is pushed right with 70 N, what is the other force?

Accepted Answer

$$F = -10\,	ext{N}$$

Question 5

According to Newton's First Law, what happens to an object if no net force acts on it?

Accepted Answer

It will remain at rest or move at constant velocity.

Question 6

Which quantity is a measure of inertia?

Accepted Answer

Mass

Question 7

A 6 kg box is pushed to the right with 20 N and to the left with 20 N. What is its acceleration?

Accepted Answer

$$a = \frac{20 - 20}{6}$$

Question 8

Which statement about mass and weight is correct?

Accepted Answer

Weight changes depending on location, but mass does not.

Question 9

What is the formula for the weight force acting on an object near Earth's surface?

Accepted Answer

$$W = m \cdot g$$

Question 10

The Mars Rover Perseverance weighed about 10,000 N on Earth and 3,790 N on Mars. What is the gravitational acceleration on Mars?

Accepted Answer

$$g_{Mars} = 3.7\,	ext{m/s}^2$$

Question 11

A 3-kg bucket is being pulled upwards by a cord with a tension of 35 N. What is the acceleration of the bucket? (Assume $$g = 9.8\,	ext{m/s}^2)$$

Accepted Answer

$$a = 1.9\,	ext{m/s}^2$$

Question 12

A 100-kg load of bricks is being lowered at 5 m/s and comes to rest in 2 s. What is the tension in the supporting cable during this interval? (Assume $$g = 9.8\,	ext{m/s}^2)$$

Accepted Answer

$$T = 1480\,	ext{N}$$

Question 13

If the upward force on an object is equal to the downward force, what is the object's acceleration?

Accepted Answer

$$a = 0$$

Question 14

According to Newton's Third Law, which statement is true?

Accepted Answer

Action and reaction forces are equal in magnitude and opposite in direction.

Question 15

You (80 kg) push a 40 kg ice block with a force of 20 N on a frictionless surface. What is the acceleration of the block?

Accepted Answer

$$a = \frac{20}{40}$$

Question 16

Which of the following is NOT an action-reaction pair?

Accepted Answer

Weight of the book & normal force on the book

Question 17

If a 10 kg object has a mass of 10 kg on Earth, what is its mass and weight on the Moon? ($$g_{moon} = 1.62\,	ext{m/s}^2)$$

Accepted Answer

Mass: 10 kg, Weight: 16.2 N

Question 18

A bathroom scale measures your 'weight' as 70 kg. What is your real weight on Earth's surface?

Accepted Answer

$$W = 70 	imes 9.8 = 686\,	ext{N}$$

Study Notes: Forces & Newton's Laws of Motion

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