Q: A 2.00 kg block is accelerated upward at 3.00 $$m/s^2 by an $$applied force F. What is the magnitude of the applied force F?

$$F = 2.00 \times (9.80 + 3.00) = 25.6\ \mathrm{N}$$

Q: A 1.00 kg mass is weighed on Earth where $$g = 9.80\ \mathrm{m/s^2$}. $$What is its weight?

$$w = mg = 1.00 \times 9.80 = 9.80\ \mathrm{N}$$

Q: A 2.00 kg block is hanging at rest from a rope. What is the tension in the rope?

$$T = mg = 2.00 \times 9.80 = 19.6\ \mathrm{N}$$

Question 1

A 2.00 kg block is accelerated upward at 3.00 $$m/s^2 by an $$applied force F. What is the magnitude of the applied force F?

Accepted Answer

$$F = 2.00 	imes (9.80 + 3.00) = 25.6\ \mathrm{N}$$

Question 2

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

Accepted Answer

For every action, there is an equal and opposite reaction: $$\vec{F}_{12} = -\vec{F}_{21}$$

Question 3

A 1.00 kg mass is weighed on Earth where $$g = 9.80\ \mathrm{m/s^2$}. $$What is its weight?

Accepted Answer

$$w = mg = 1.00 	imes 9.80 = 9.80\ \mathrm{N}$$

Question 4

If a Hummer and a Mini-Cooper are both pushed with the same force, which will have the greater acceleration?

Accepted Answer

The Mini-Cooper, because $$a = \frac{F_{net}}{m}$$ and it has less mass.

Question 5

A block is pulled to the right at constant velocity across a table with friction. What can you say about the net force on the block?

Accepted Answer

The net force is zero: $$\sum F_i = 0$$

Question 6

Which of the following is NOT a correct step in drawing a free-body diagram?

Accepted Answer

Include forces that the object exerts on other objects.

Question 7

A 2.00 kg block is hanging at rest from a rope. What is the tension in the rope?

Accepted Answer

$$T = mg = 2.00 	imes 9.80 = 19.6\ \mathrm{N}$$

Question 8

A block is moving to the right at constant velocity on a table. There is friction between the block and the table. What is the direction of the friction force?

Accepted Answer

To the left, opposite to the direction of motion.

Question 9

If the net force on an object is zero, what can you conclude about its motion?

Accepted Answer

Its velocity is constant: $$\frac{d\vec{v}}{dt} = 0$$

Question 10

A person pulls horizontally on block B, which is stacked with block A on top. Both move to the right at constant velocity. There is friction between block B and the table, but not between A and B. What is the horizontal force that B exerts on A?

Accepted Answer

Zero, because there is no friction between A and B.

Question 11

Why is it important to mention friction between block B and the table in a problem where blocks are moving at constant velocity?

Accepted Answer

Because otherwise there would be a net force and the blocks would not move at constant velocity.

Question 12

A block is pulled to the right at constant velocity, but now there is air resistance (drag force) in addition to friction. What is the direction of the force that block B exerts on block A?

Accepted Answer

To the right, because air resistance acts on both blocks.

Question 13

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

Accepted Answer

$$\vec{a} = \frac{\vec{F}_{net}}{m}$$

Question 14

A block is falling freely under gravity. What is the net force acting on it?

Accepted Answer

$$\vec{F}_{net} = m \vec{g}$$

Question 15

Which of the following is an action-reaction pair according to Newton's Third Law?

Accepted Answer

The force of the earth on an apple and the force of the apple on the earth.

Question 16

A block is at rest on a table. Which statement is true about the forces acting on the block?

Accepted Answer

The normal force and the weight are equal in magnitude and opposite in direction.

Question 17

Can an object be in equilibrium when only one force acts on it?

Accepted Answer

No, because equilibrium requires the net force to be zero, which is only possible if all forces cancel.

Question 18

A 5.0 kg object is on the Moon, where $$g_{moon} = 1.62\ \mathrm{m/s^2$}. $$What is its weight on the Moon?

Accepted Answer

$$w = 5.0 	imes 1.62 = 8.1\ \mathrm{N}$$

Question 19

A block is being pulled upward by a rope with a force greater than its weight. What is the direction of its acceleration?

Accepted Answer

Upward, because the net force is upward.

Newton’s Laws of Motion, Mass, Weight, and Free-Body Diagrams

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