Physics Ch 9

The Moon's gravitational pull is _________.

strongest on the side of Earth closest to the Moon.

The factor most directly responsible for making a black hole invisible is its

surface escape velocity.

Newton discovered

that gravity is universal.

Which is most responsible for the ocean tides?

the moon.

Black holes are essentially _______.

collapsed stars

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

increases.

A hollow spherical planet is inhabited by people who live inside it, where the gravitational field is zero. When a very massive space ship lands on the planet's surface, inhabitants find that the gravitational field inside the planet is

non-zero, directed towards the spaceship.

Consider two planets in space that gravitationally attract each other. If the masses of both planets are doubled, and the distance between them is also doubled, then the force between them is

none of these.

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

practically the same weight.

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

remains the same.

A black hole is

simply the remains of a giant star that has undergone gravitational collapse.

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

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

Which pulls on the oceans of the Earth with the greater force?

the sun.

Each day _______________.

there are two high tides and two low tides

An asteroid exerts a 360-N gravitational force on a nearby spacecraft. This force is directed

toward the asteroid.

A high tide can occur __________.

when the Moon is high overheard.

Is gravitational force acting on a person who falls off a cliff?

yes

Is gravitational force acting on an astronaut inside an orbiting space shuttle?

yes

Half way to the center of a completely hollow planet with a thin uniform shell, your weight would be

zero.

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

500 N.

Approximately how much time passes between low and high tide?

6 hours.

How far must one travel to get away from the Earth's gravitational field?

Forget it; you can't travel far enough.

Imagine that the Sun could be turned into a black hole without changing its mass. How would Earth's orbit change?

Earth's orbit would not change.

An object is placed exactly halfway between the Earth and moon. The object will fall toward the

Earth.

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

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

What happens to the force of attraction between two planets when the distance between them is doubled?

The force decreases to one quarter.

How do the high tides during a full moon compare to high tides during a new moon?

The high tides during a full moon are roughly the same as the high tides during a new moon.

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?

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

If there were no Moon, would there still be tides on Earth?

Yes, because the Sun's gravity still has an influence.

Inside a freely falling runaway elevator, your

apparent weight is zero.

Which of the following lists correctly gives, in increasing order, the height of the high tides that occur during particular lunar phases? (Ties are denoted by parentheses.)

(first quarter, third quarter), (new, full)

No force due to Earth's gravity is acting on the astronauts inside the orbiting space shuttle. This statement is

always false.

The Earth's gravitational field extends

both inside and outside the Earth and throughout the entire universe.

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

eliminates the role of force

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

100 N.

Find the change in the gravitational force between two planets if the masses of both planets are doubled but the distance between them stays the same.

4

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

40 N.

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

accelerate as you fall and cross the event horizon completely unhindered

The amount of gravitational force that acts on the space shuttle while in orbit is

almost as much as the shuttle's weight on the Earth's surface.

Inside a freely falling elevator, there would be no

apparent weight for you.

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

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

According to Newton, doubling the distance between two interacting objects

divides by 4 the gravitational force between them.

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

increase also.

The main reason ocean tides exist is that the pull of the moon

is greater on oceans closer to the moon and less on oceans farther from the moon.