$$F = 1000 \times 2 = 2000\ \mathrm{N}$$

$$W = 10 \times 9.8 = 98\ \mathrm{N}$$

$$F = 3 \times 4 = 12\ \mathrm{N}$$

Question 1

A 5 kg box is pushed across a rough floor with a net force of 15 N. What is its acceleration?

Accepted Answer

$$a = \frac{15}{5} = 3\ \mathrm{m/s^2$}$$

Question 2

Which of the following best explains why a heavy and a light object fall at the same rate in a vacuum?

Accepted Answer

The heavier object has more weight but also more inertia, so these effects cancel out.

Question 3

A car of mass 1000 kg accelerates at $$2\ \mathrm{m/s^2$}. $$What is the net force acting on the car?

Accepted Answer

$$F = 1000 	imes 2 = 2000\ \mathrm{N}$$

Question 4

If the net force on an object is doubled and its mass is also doubled, what happens to its acceleration?

Accepted Answer

Acceleration remains the same.

Question 5

A skydiver falls faster and faster through the air. What happens to the air resistance acting on them?

Accepted Answer

Air resistance increases.

Question 6

A 10 kg object weighs how many newtons on Earth's surface? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$W = 10 	imes 9.8 = 98\ \mathrm{N}$$

Question 7

When Sanjay pushes a refrigerator across a kitchen floor at a constant speed, the force of friction between the refrigerator and the floor is:

Accepted Answer

Equal and opposite to Sanjay's push.

Question 8

Which surface will produce the highest friction when a metal block is placed on it?

Accepted Answer

Sandpaper

Question 9

A 20-N falling object encounters 5 N of air resistance. What is its acceleration? (Use $$g = 10\ \mathrm{m/s^2$})$$

Accepted Answer

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

Question 10

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

Accepted Answer

It is halved.

Question 11

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

Accepted Answer

They fall together side by side.

Question 12

A 5-kg iron ball and a 10-kg iron ball are dropped from rest. For negligible air resistance, the acceleration of the heavier ball will be:

Accepted Answer

The same as the lighter ball.

Question 13

Which of the following is NOT an example of friction?

Accepted Answer

A ball floating in space far from any object.

Question 14

A skydiver reaches terminal velocity. What is true about the forces acting on them?

Accepted Answer

The upward air resistance equals the downward weight.

Question 15

A 3 kg ball accelerates at $$4\ \mathrm{m/s^2$}. $$What is the force applied?

Accepted Answer

$$F = 3 	imes 4 = 12\ \mathrm{N}$$

Question 16

When the string is pulled down quickly and the bottom string breaks, which property of the ball does this best illustrate?

Accepted Answer

Mass of the ball

Question 17

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

Accepted Answer

Mass is independent of gravity, while weight depends on gravity.

Question 18

A basketball player jumps straight up and is in the air for $$0.80$$ seconds. Approximately how high did she jump? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$h = \frac{1}{2} g t^2$ = \frac{1}{2} 	imes 9.8 	imes (0.4)^2$ \approx 0.78\ \mathrm{m}$$

Question 19

Why do car tires have tread?

Accepted Answer

To increase friction with the road for better control and safety.

Newton's Second Law of Motion: Acceleration, Friction, Free Fall, and Non-Free Fall

스터디 가이드 - 연습 문제