Mastering Astronomy Homework 9

As you watch the video, notice that the size of the tidal bulges varies with the Moon's phase, which depends on its orbital position relative to the Sun. Which of the following statement(s) accurately describe(s) this variation?

-Low tides are lowest at both full moon and new moon. -High tides are highest at both full moon and new moon.

As shown in the video, Earth has two tidal bulges at all times. Approximately where are these bulges located?

One faces the Moon and one faces opposite the Moon.

You have found that tides on Earth are determined primarily by the position of the Moon, with the Sun playing only a secondary role. Why does the Moon play a greater role in causing tides than the Sun?

because the gravitational attraction between Earth and the Moon varies more across Earth than does the gravitational attraction between Earth and the Sun

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

As a giant cloud of gas collapses due to gravity, you would expect its rate of rotation to

increase

Why are astronauts (and other objects) weightless inside the International Space Station as it orbits Earth?

they are in free-fall

Any particular location on Earth experiences __________.

two high tides and two low tides each day

Which of the following statements correctly state general principles of motion? (Assume that the moving object's mass is not changing.) Select all that apply .

-An object that is accelerating is also being acted upon by a (nonzero) net force -An object that is accelerating is also undergoing a change in momentum. -An object that is accelerating is also undergoing a change in momentum.

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

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

the force you exert on the scale

Which of the following are allowed orbital paths under gravity? Select all that apply.

-hyperbolic -elliptical -parabolic

If you actually performed and compared the two trials chosen in Part C, you would find that, while the basketball and marble would hit the ground at almost the same time, it would not quite be exact: The basketball would take slightly longer to fall to the ground than the marble. Why?

Because air resistance has a greater effect on the larger ball

Assume you have completed the two trials chosen in Part A. Which of the following possible outcomes from the trials would support Newton's theory of gravity? Neglect effects of air resistance.

Both balls fall to the ground in the same amount of time

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 __________.

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

One tidal bulge faces toward the Moon because that is where the gravitational attraction between Earth and the Moon is strongest. Which of the following best explains why there is also a second tidal bulge?

The second tidal bulge arises because gravity weakens with distance, essentially stretching Earth along the Earth-Moon line

Suppose you drive from home to your child's school, pick her up, and drive back home, covering a total distance of 25 miles in 1 hour. Which of the following statements are true? Select all the true statements.

-Your average speed for the trip is 25 miles per hour. -You must accelerate when you reach the school. -Your velocity is different on the return home than it is on the way to school.

Which of the following represents a change from potential energy to kinetic energy?

A rock starting from rest on a high cliff, then moving faster and faster as it falls.

Einstein's theory, like Newton's, predicts that, in the absence of air resistance, all objects should fall at the same rate regardless of their masses. Consider the following hypothetical experimental results. Which one would indicate a failure of Einstein's theory?

Scientists dropping balls on the Moon find that balls of different mass fall at slightly different rates.

In Part A, you found that your weight will be greater than normal when the elevator is moving upward with increasing speed. For which of the following other motions would your weight also be greater than your normal weight?

The elevator moves downward while slowing in speed.

Most people are familiar with the rise and fall of ocean tides. Do tides also affect land?

Yes, though land rises and falls by a much smaller amount than the oceans.

Suppose you are in an elevator car when the elevator cable breaks. Which of the following correctly describes what happens and why.

You float weightlessly within the elevator car because you and the elevator both begin to accelerate downward at the same rate.

Suppose two objects are attracting each other gravitationally. If you double the distance between them, the strength of their gravitational attraction __________.

decreases by a factor of 4