Chapter 4

Question 1

Which of the following represents a case in which you are not accelerating?
Slamming on the brakes to come to a stop at a stop sign
Driving in a straight line at 60 miles per hour
Driving 60 miles per hour around a curve
Going from 0 to 60 miles per hour in 10 seconds

Answer 1

Driving in a straight line at 60 miles per hour

Question 2

Suppose you drop a 10-pound weight and a 5-pound weight on the Moon, both from the same height at the same time. What will happen?

Answer 2

Both will hit the ground at the same time.

Question 3

Why are astronauts weightless in the Space Station?

Answer 3

Because the Space Station is constantly in free-fall around the Earth

Question 4

A net force acting on an object will always cause a change in the object’s _________.

Answer 4

momentum

Question 5

Suppose you are in an elevator that is traveling upward at constant speed. How does your weight compare to your normal weight on the ground?

Answer 5

it is the same

Question 6

The planets never travel in a straight line as they orbit the Sun. According to Newton’s second law of motion, this must mean that _________.

Answer 6

a force is acting on the planets

Question 7

Suppose the Sun were suddenly to shrink in size but that its mass remained the same. According to the law of conservation of angular momentum, what would happen?

Answer 7

The Sun would rotate faster than it does now

Question 8

Suppose you kick a soccer ball straight up to a height of 10 meters. Which of the following is true about the gravitational potential energy of the ball during its flight?
The ball’s gravitational potential energy is greatest at the instant when the ball is at its highest point.
The ball’s gravitational potential energy is always the same.
The ball’s gravitational potential energy is greatest at the instant the ball leaves your foot.
The ball’s gravitational potential energy is greatest at the instant it returns to hit the ground.

Answer 8

The ball’s gravitational potential energy is greatest at the instant when the ball is at its highest point.

Question 9

Suppose you heat an oven to 400°F and boil a pot of water. Which of the following explains why you would be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven?

Answer 9

The water can transfer heat to your arm more quickly than the air.

Question 10

Which of the following scenarios involves energy that we would typically calculate with Einstein’s formula E=mc 2?

Answer 10

A small amount of the hydrogen in of a nuclear bomb becomes energy as fusion converts the hydrogen to helium.

Question 11

A rock held above the ground has potential energy. As the rock falls, this potential energy is converted to kinetic energy. Finally, the rock hits the ground and stays there. What has happened to the energy?

Answer 11

The energy goes to producing sound and to heating the ground, rock, and surrounding air.

Question 12

Suppose that the Sun shrank in size but that its mass remained the same. What would happen to the orbit of the Earth?

Answer 12

Earth’s orbit would be unaffected.

Question 13

Imagine another solar system, with a star of the same mass as the Sun. Suppose a planet with a mass twice that of Earth (2M Earth) orbits at a distance of 1 AU from the star. What is the orbital period of this planet?

Answer 13

1 year

Question 14

Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet’s year (orbital period) compare to Earth’s year?

Answer 14

The planet’s year would be shorter than Earth’s.

Question 15

Newton showed that Kepler’s laws are _________.

Answer 15

natural consequences of the law of universal gravitation

Question 16

Each of the following lists two facts. Which pair of facts can be used with Newton’s version of Kepler’s third law to determine the mass of the Sun?

Answer 16

Earth is 150 million km from the Sun and orbits the Sun in one year.

Question 17

When space probe Voyager 2 passed by Saturn, its speed increased (but not due to firing its engines). What must have happened?

Answer 17

Saturn must have lost a very tiny bit of its orbital energy

Question 18

Suppose that a lone asteroid happens to be passing Jupiter on an unbound orbit (well above Jupiter’s atmosphere and far from all of Jupiter’s moons.) Which of the following statements would be true?

Answer 18

The asteroid’s orbit around Jupiter would not change, and it would go out on the same unbound orbit that it came in on.

Question 19

what describes the origin of ocean tides on Earth?

Answer 19

Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the Earth.

Question 20

At which lunar phase(s) are tides most pronounced (for example, the highest high tides)?

Answer 20

both new and full moons

Question 21

why are the Moon’s orbital period and rotation period are the same?

Answer 21

The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period

Question 22

The difference between speed and velocity is that _________.

Answer 22

velocity also includes a direction

Question 23

The acceleration of gravity on Earth is approximately 10 m/s2 (more precisely, 9.8 m/s2). If you drop a rock from a tall building, about how fast will it be falling after 3 seconds?

Answer 23

30m/s

Question 24

Momentum is defined as _________.

Answer 24

mass times velocity

Question 25

Suppose you lived on the Moon. Which of the following would be true?

Answer 25

Your weight would be less than your weight on Earth, but your mass would be the same as it is on Earth.

Question 26

In which of the following cases would you feel weightless?

Answer 26

while falling from a roof

Question 27

Which of the following statements is not one of Newton’s Laws of Motion?

Answer 27

what goes up must come down

Question 28

Newton’s Second Law of Motion tells us that the net force applied to an object equals its _________.

Answer 28

mass times accleration

Question 29

Suppose that two objects collide. Which of the following things is not the same both before and after the collision?

Answer 29

the total temperature of the objects

Question 30

When a spinning ice skater pulls in his arms, he spins faster because _________.

Answer 30

his angular momentum must be conserved, so reducing his radius must increase his speed of rotation

Question 31

The energy attributed to an object by virtue of its motion is known as _________.

Answer 31

kinetic energy

Question 32

Radiative energy is _________.

Answer 32

energy carried by light

Question 33

Absolute zero is _________.

Answer 33

0 kelvin

Question 34

What does temperature measure?

Answer 34

The average kinetic energy of particles in a substance

Question 35

In the formula E=mc 2, what does E represent?

Answer 35

The mass-energy, or potential energy stored in an object’s mass

Question 36

According to the universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them _________.

Answer 36

decreases by a factor of 9

Question 37

What is the difference between a bound orbit and an unbound orbit around the Sun?

Answer 37

An object on a bound orbit follows the same path around the Sun over and over, while an object on an unbound orbit approaches the Sun just once and then never returns.

Question 38

Why is Newton’s version of Kepler’s third law so useful to astronomers?

Answer 38

it can be used to determine the mass of many distant objects

Question 39

What do we mean by the orbital energy of an orbiting object (such as a planet, moon, or satellite)?

Answer 39

Orbital energy is the sum of the object’s kinetic energy and its gravitational potential energy as it moves through its orbit.

Question 40

Which statement must be true in order for a rocket to travel from Earth to another planet?

Answer 40

It must attain escape velocity from Earth.

Question 41

Approximately where is it currently high tide on Earth?

Answer 41

On the portion of Earth facing directly toward the Moon and on the portion of Earth facing directly away from the Moon