HW Ch 4

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

A. One faces the Moon and one faces the Sun. B. One faces the Moon and one faces opposite the Moon. C. Both are on lines perpendicular to the Earth-Moon line. D. One is over the Atlantic Ocean, and one is over the Pacific Ocean.

If the Moon were closer to Earth, high tides would: A

A. be higher than they are now. B. be lower than they are now. C. occur three or more times a day rather than twice a day.

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 __________. A

A. less than your normal weight at rest B. greater than your normal weight at rest C. equal to your normal weight at rest

The following diagrams are the same as those from Part A. This time, rank the five positions of the spaceship from left to right based on the strength of the gravitational force that the Moon exerts on the spaceship, from strongest to weakest.

Ranking goes from closest to the Moon to the furthest from the Moon. (Gravity follows an inverse square law with distance, which means the force of gravity between the Moon and the spaceship increases as the spaceship approaches the Moon.)

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? A, D

A. Low tides are lowest at both full moon and new moon. B. High tides are highest at first- and third-quarter moon. C. High tides are highest at full moon and lowest at new moon. D. Low tides are highest at full moon and lowest at new moon. E. High tides are highest at both full moon and new moon. F. Low tides are highest at both full moon and new moon.

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

A. No, tides only affect the oceans. B. Yes, land rises and falls with tides equally as high (and low) as the oceans. C. Yes, though land rises and falls by a much smaller amount than the oceans. D. No, tides can only affect liquids and gases, not solids.

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

A. You float weightlessly within the elevator car because Earth's gravity is no longer tugging on you. B. You will remain stuck to the elevator floor as you and the elevator plunge downward toward a horrific crash. C. You float weightlessly within the elevator car because you and the elevator both begin to accelerate downward at the same rate. D. You will crash your head into the elevator car ceiling because the car will be falling rapidly away from you. E. You will crash your head into the elevator car ceiling because Earth's gravity will be pulling the car down faster than it pulls you down.

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? C

A. because the gravitational force between Earth and the Moon is stronger than the gravitational force between Earth and the Sun B. because the Moon orbits Earth faster than Earth orbits the Sun C. because the gravitational attraction between Earth and the Moon varies more across Earth than does the gravitational attraction between Earth and the Sun

If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be: C

A. twice as strong. B. half as strong. C. one-quarter as strong.

Any particular location on Earth experiences __________. D

A. two sets of high and low tides in the ocean, but only one set on land B. two high tides and two low tides each month C. one high tide and one low tide each day D. two high tides and two low tides each day E.one high tide and one low tide each month

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

A. your mass B. the force you exert on the scale C. the gravitational force exerted on you by Earth

Compared to their values on Earth, on another planet, C

A. your weight would be the same but your mass would be different. B. your mass and weight would both be the same. C. your mass would be the same but your weight would be different.

Which of the cars is accelerating? B

A. A car traveling on a straight, flat road at 50 miles per hour. B. A car going around a circular track at a steady 100 miles per hour. C. A car traveling on a straight uphill road at 30 miles per hour.

Which person is weightless? A

A. A child in the air as she plays on a trampoline. B. A scuba diver exploring a deep-sea wreck. C. An astronaut on the Moon.

Compared to its angular momentum when it is farthest from the Sun, Earth's angular momentum when it is nearest to the Sun is: B

A. greater B. the same C. less

Compare the Sun's annual energy output to the energy released by a supernova.

E_supernova / E_sun ~ 10^11

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 __________. B

A. Earth has a larger acceleration than the Moon, because it has a larger mass B. the Moon has a larger acceleration than Earth, because it has a smaller mass C. the Moon and Earth both have equal accelerations, because the forces are equal

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 __________. B

A. less than your normal weight at rest B. greater than your normal weight at rest C. equal to your normal weight at rest

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? E

A. The elevator moves downward while increasing in speed. B. The elevator moves downward with constant velocity. C. The elevator moves upward with constant velocity. D. The elevator moves upward while slowing in speed. E. The elevator moves downward while slowing in speed.

Someday soon, scientists are likely to build an engine that produces more energy than it consumes.

False This statement does not make sense, because such an engine would violate the law of conservation of energy.

Consider the statement "There's no gravity in space." This statement is: A

A. Completely false. B. False if you are close to a planet or moon, but true in between the planets. C. Completely true.

The following five diagrams show pairs of astronomical objects that are all separated by the same distance ddd. Assume the asteroids are all identical and relatively small, just a few kilometers across. Considering only the two objects shown in each pair, rank the strength, from strongest to weakest, of the gravitational force acting on the asteroid on the left.

Sun, Earth, Moon, asteroid, hydrogen atom

The following diagrams are the same as those from Part A. Again considering only the two objects shown in each pair, this time rank the strength, from strongest to weakest, of the gravitational force acting on the object on the right.

Sun, Earth, Moon, asteroid, hydrogen atom (Newton's third law tells us that the gravitational force exerted on the asteroid on the left by the object on the right will be equal in magnitude, but opposite in direction to the gravitational force exerted on the object on the right by the asteroid on the left. That is why the ranking here is the same as the ranking for Part A.)

Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once.

1. The light from Polaris travels through space in the form of radiative energy. 2. Rapidly moving comets have more kinetic energy than slowly moving ones. 3. An apple contains chemical potential energy that your body can convert into other forms energy. 4. Nuclear fusion in stars converts some of the mass-energy of hydrogen nuclei into light and heat. 5. Due to its much higher density, water heated to 80 degrees (Celsius) contains more thermal energy than air at the same temperature. 6. An asteroid that is moving farther from the Sun is gaining gravitational potential energy.

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? D

A. The second tidal bulge is a rebound effect, created when water on the side facing the Moon falls back down and thereby pushes up the water on the opposite side of Earth. B. The second tidal bulge is created by the centrifugal force caused by Earth's rapid rotation. C. The second tidal bulge is created by the Sun's gravity. D. The second tidal bulge arises because gravity weakens with distance, essentially stretching Earth along the Earth-Moon line.

What is free-fall, and why does it make you weightless? Briefly describe why astronauts are weightless in the Space Station.

Free-fall is the state of falling without any resistance to the fall. Objects in free-fall are weightless because they are not pushing against anything to give them weight. Astronauts in the Space Station are in constant free-fall as they fall around the Earth (always missing it), so they are weightless.

Each of the following diagrams shows a spaceship somewhere along the way between Earth and the Moon (not to scale); the midpoint of the distance is marked to make it easier to see how the locations compare. Rank the five positions of the spaceship from left to right based on the strength of the gravitational force that Earth exerts on the spaceship, from strongest to weakest. (Assume the spaceship has the same mass throughout the trip; that is, it is not burning any fuel.)

Ranking goes from furthest from the Moon to the closest to the Moon. (Gravity follows an inverse square law with distance, which means the force of gravity between Earth and the spaceship weakens as the spaceship gets farther from Earth.)

The following diagrams show five pairs of asteroids, labeled with their relative masses (M) and distances (d) between them. For example, an asteroid with M=2 has twice the mass of one with M=1 and a distance of d=2 is twice as large as a distance of d=1. Rank each pair from left to right based on the strength of the gravitational force attracting the asteroids to each other, from strongest to weakest.

Strongest M_1=2, M_2 = 2, d = 1 M_1=1, M_2 = 2, d = 1 M_1=1, M_1 = 2, d = 1 M_1=1, M_2 = 2, d = 2 M_1=1, M_2 = 1, d = 2 Weakest

The following diagrams are the same as those from Part A. This time, rank the pairs from left to right based on the size of the acceleration the asteroid on the left would have due to the gravitational force exerted on it by the object on the right, from largest to smallest.

Sun, Earth, Moon, asteroid, hydrogen atom (According to Newton's second law, the asteroid with the largest acceleration will be the one that has the strongest gravitational force exerted on it by the object on the right.)