Chapter 5

If you drop a ball from rest it will fall 5 meters in one second. If you toss the ball horizontally it will fall in one second a vertical distance of

5 m.

When the distance between two planets is doubled, the force of attraction between them

decreases to one quarter.

When the masses of two planets are doubled, the force of attraction between them

quadruples.

One's weightlessness in space involves no

support force.

If you are standing on a scale in an elevator, what exactly does the scale measure?

the force you exert on the scale

The crew of a cargo plane wishes to drop a crate of supplies on a target below. To hit the target, when should the crew drop the crate? Ignore air resistance.

Before the plane is directly over the target

Which is gravitationally attracted to Earth: an apple, the Moon, or both?

Both are gravitationally attracted to the Earth!

Is gravitational force acting on a person who falls off a cliff? Is it acting on an astronaut inside an orbiting space vehicle?

Gravitational force is acting on a person who falls off a cliff, and the force is acting on a person in a space vehicle.

Why does the gravity in the Space Shuttle compare with the gravity on Earth the way it does?

The Space Shuttle and the surface of the Earth are about the same distance from the center of the Earth.

Why do the astronauts in the Space Shuttle float around?

The Space Shuttle is in free fall, so the shuttle and the astronauts inside it are continuously falling toward the Earth. They thus experience apparent weightlessness.

Which ball (if either) has the greatest speed at the moment of impact?

The ball thrown horizontally

Assume that you weight yourself on a bathroom scale. Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was moving downward at constant velocity?

The compression of the springs would be unchanged

Assume that you weight yourself on a bathroom scale. Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was moving upward at constant velocity?

The compression of the springs would be unchanged.

What is the effect of air drag on the height and range of batted baseballs?

The effect of air drag is that both range and height are decreased.

As you found in Part A, your weight will be greater than normal when the elevator is moving upward with increasing speed. For what other motion would your weight also be greater than your normal weight?

The elevator moves downward while slowing in speed.

How does the gravity in the Space Shuttle compare with the gravity on Earth's surface?

The gravity in the Space Shuttle is approximately equal to the gravity on the surface of the Earth.

When is your weight equal to mg?

When you are in a state of zero acceleration on the Earth's surface.

When is your weight greater than mg?

When you are in an elevator that accelerates upward near the Earth's surface.

When is your weight zero?

When you are in free fall.

Is it possible to simulate weight in a space habitat?

Yes, weight can be simulated with the centripetal force acting on a person moving in a circular path.

If Earth somehow expanded to a larger radius, with no change in mass, how would your weight be affected?

Your weight would decrease as you become farther from the center of Earth.

Occupants in a rotating donut-like space habitat experience weight due to

a support force.

Consider the video you just watched. Suppose we replace the original launcher with one that fires the ball upward at twice the speed. We make no other changes. How far behind the cart will the ball land, compared to the distance in the original experiment?

four times as far

Suppose you are in an elevator. As the elevator starts upward, its speed will increase. During this time when the elevator is moving upward with increasing speed, your weight will be __________.

greater than your normal weight at rest

The constant G in Newton's equation for universal gravitation

makes the units of measurement consistent.

Suppose you are in an elevator that is moving upward. As the elevator nears the floor at which you will get off, its speed slows down. During this time when the elevator is moving upward with decreasing speed, your weight will be __________.

less than your normal weight at rest

Is it correct to say that the planets of the solar system are simply projectiles falling around the Sun?

yes