Q: A 10 kg object on Earth weighs approximately:

$$W = mg = 10\ \mathrm{kg} \times 9.8\ \mathrm{m/s^2$} = 98\ \mathrm{N}$$

Question 1

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

Accepted Answer

An object at rest will remain at rest and an object in motion will remain in motion at constant speed in a straight line unless acted upon by an outside force.

Question 2

A 5 kg object is acted upon by a net force of 20 N. What is its acceleration?

Accepted Answer

$$a = \frac{F}{m} = \frac{20}{5} = 4\ \mathrm{m/s^2$}$$

Question 3

If you double the mass of an object but keep the net force the same, what happens to its acceleration?

Accepted Answer

The acceleration is halved.

Question 4

A skydiver of weight 800 N falls through the air and eventually reaches terminal velocity. What is the magnitude of the air resistance at terminal velocity?

Accepted Answer

800 N

Question 5

Which statement about mass and weight is correct?

Accepted Answer

Mass is the quantity of matter in an object, while weight is the force due to gravity acting on that mass.

Question 6

A 2 kg object falls and encounters 5 N of air resistance. What is its acceleration?

Accepted Answer

$$a = \frac{F_{net}}{m} = \frac{20\ \mathrm{N} - 5\ \mathrm{N}}{2\ \mathrm{kg}} = 7.5\ \mathrm{m/s^2$}$$

Question 7

When a crate is pushed across a rough floor at constant speed, the force of friction is:

Accepted Answer

Equal and opposite to the push force.

Question 8

If a skydiver continues to fall faster and faster through the air, what happens to the net force acting on them?

Accepted Answer

It decreases.

Question 9

A 10 kg object on Earth weighs approximately:

Accepted Answer

$$W = mg = 10\ \mathrm{kg} 	imes 9.8\ \mathrm{m/s^2$} = 98\ \mathrm{N}$$

Question 10

If a 5 kg iron ball and a 10 kg iron ball are dropped from rest in a vacuum, which will hit the ground first?

Accepted Answer

Both will hit at the same time.

Question 11

A person pulls down slowly on a string attached to a hanging ball, and the top string breaks. This best illustrates:

Accepted Answer

The weight of the ball.

Question 12

A person pulls down quickly on a string attached to a hanging ball, and the bottom string breaks. This best illustrates:

Accepted Answer

The mass of the ball.

Question 13

If the mass of an object is halved, what happens to its weight?

Accepted Answer

It is halved.

Question 14

A rocket in space expels gas backward. What is the reaction force according to Newton's Third Law?

Accepted Answer

The force of the expelled gas pushing the rocket forward.

Question 15

A 50-N person falls at terminal speed. What is the air resistance acting on the person?

Accepted Answer

50 N.

Question 16

Which of the following factors does NOT affect the force of friction between two surfaces?

Accepted Answer

The speed at which the surfaces move past each other.

Question 17

A coin and a feather are dropped in a vacuum. What happens?

Accepted Answer

Both fall together at the same rate.

Question 18

A skydiver jumps from a plane. As she falls faster and faster, what happens to the air resistance?

Accepted Answer

It increases.

Question 19

At the instant an object in free fall has a speed of 40 m/s, what will its speed be 1 second later (assuming $$g = 10\ \mathrm{m/s^2$}$$ downward)?

Accepted Answer

$$50\ \mathrm{m/s}$$

Newton's Laws of Motion, Friction, Mass, Weight, and Terminal Velocity

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