chapter9

Question 1

What happens to the force of attraction between two planets when the masses of both are doubled?

Answer 1

force quadruples

Question 2

What is the magnitude of the gravitational force between two 1-kg bodies that are 1 m apart?

Answer 2

6.67 × 10 -11 N

Question 3

What is the magnitude of Earth’s gravitational force on a 1-kg body at Earth’s surface?

Answer 3

10N

Question 4

How does the force of gravity between two bodies change when the distance between them is doubled?

Answer 4

The force decreases to ¼ of its initial value

Question 5

Describe how the gravitational forces from the Sun and the Moon compare from one side of Earth to the other.

Answer 5

The Sun exerts a stronger force on the side of Earth nearest the Sun, and the Moon exerts a stronger force on the side nearest the Moon.

Question 6

According to Newton, the greater the masses of interacting objects, the

Answer 6

greater the gravitational force between them.

Question 7

According to Newton, when the distance between two interacting objects doubles, the gravitational force is

Answer 7

1/4

Question 8

If Earth’s radius somehow increased with no change in mass, your weight would

Answer 8

decrease

Question 9

If the mass of Earth somehow increased with no change in radius, your weight would

Answer 9

increase also

Question 10

A very massive object A and a less massive object B move toward each other under the influence of gravity. Which force, if either, is greater?

Answer 10

both forces are the same

Question 11

Two objects move toward each other due to gravity. As the objects get closer and closer, the force between them

Answer 11

increases

Question 12

The force of Earth’s gravity on a capsule in space will lessen as it moves farther away. If the capsule moves to twice its distance, the force toward Earth becomes

Answer 12

1/4

Question 13

The force of Earth’s gravity on a capsule in space increases as it comes closer. When the capsule moves to half its distance, the force toward Earth is then

Answer 13

four times greater

Question 14

When the distance between two stars decreases by one-third, the force between them

Answer 14

increases to nine times as much

Question 15

A weight watcher who normally weighs 400 N stands on top of a very tall ladder so she is one Earth radius above Earth’s surface. How much is her weight there?

Answer 15

100 N

Question 16

Which is most responsible for Earth’s ocean tides?

Answer 16

moon

Question 17

The main reason ocean tides exist is that Moon’s pull is stronger

Answer 17

on water closer to it than on water farther away

Question 18

Tidal forces in general are the result of

Answer 18

unequal forces acting on different parts of a body.

Question 19

One side of the Moon continually facing Earth is

Answer 19

tidal lock

Question 20

Calculate the force of gravity on the 1-kg
mass if it were 3.2×10^6m
above Earth’s surface (that is, if it were one and a half Earth radii from Earth’s center).

Answer 20

4.3 N

Question 21

Why are all tides greatest at the time of a full Moon or new Moon?

Answer 21

At full Moon and new Moon, the tides from the Moon and the Sun add because they are in line with Earth

Question 22

Which two factors mainly affect ocean tides on Earth?

Answer 22

the moon and the sun

Question 23

Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton’s second law of motion __________.

Answer 23

the Moon has a larger acceleration than Earth, because it has a smaller mass

Question 24

In what sense does the Moon “fall”?

Answer 24

It falls away from the straight path that it would follow if there were no forces acting on it.

Question 25

Which has the higher tides: spring tides or neap tides? Why?

Answer 25

Spring tides are higher, because the tides from the Moon and Sun add together.

Question 26

If Earth shrank, but there was no change in its mass, then what would happen to your weight at the surface?

Answer 26

increase

Question 27

Earth's gravitational field is strongest at _______.

Answer 27

Earth's surface

Question 28

Why is a black hole invisible?

Answer 28

The escape velocity of the black hole is greater than the speed of light.

Question 29

Einstein's theory of gravitation, compared with Newton's, _______.

Answer 29

eliminates the role of force

Question 30

From the viewpoint of an observer in the orbiting rocket, what happens to time on the other rocket as it falls toward the event horizon of the black hole?

Answer 30

Time runs increasingly slower as the rocket approaches the black hole.

Question 31

As the falling rocket plunges toward the event horizon, an observer in the orbiting rocket would see that the falling rocket __________.

Answer 31

slows down as it approaches the event horizon and never actually crosses the event horizon

Question 32

you know that from afar you’ll never see the in-falling rocket cross the event horizon, yet it will still eventually disappear from view. Why?

Answer 32

Its light will become so redshifted that it will be undetectable.

Question 33

If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________.

Answer 33

at a constant, normal rate as you approach the event horizon

Question 34

If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________.

Answer 34

accelerate as you fall and cross the event horizon completely unhindered

Question 35

Black holes are essentially _______.

Answer 35

collapsed stars

Question 36

What is the force of gravity on a 500-N woman standing on Earth's surface?

Answer 36

500 N

Question 37

Two planets in space gravitationally attract each other. If both the masses and distances are doubled, the force between them is

Answer 37

none

Question 38

Tides caused mainly by the Moon occur in Earth's

Answer 38

oceans. interior. atmosphere

Question 39

The concept of force is fundamental to

Answer 39

Newton's theory of gravitation

Question 40

An asteroid exerts a 360-N gravitational force on a nearby spacecraft. If the spacecraft moves to a position three times as far from the center of the asteroid, the force will be

Answer 40

40 N

Question 41

When a star collapses to form a black hole, its mass

Answer 41

remains the same