Astronomy 101 Thought Questions - Spring 2013

Thought Questions for Astronomy 101 (Spring 2013)
Instructor: Eric Sandquist


Animations of Earth Seasons

Animations of Moon Phases

Animations of Retrograde Motion

Animations of Kepler's Laws

Animations of Newton's Laws


Question Topics:

Compass Directions
Seasons
Planet Motions in the Sky
Motion and Newton's Laws
Rising and Setting
Moon Phases
Kepler's Laws
Gravity
Time of Day
Eclipses
Models of the Universe

Compass Directions

If you are standing on Earth and facing due south, which of the following is true?

  1. East is to your left and west is to your right.
  2. West is to your left and east is to your right.
  3. Neither of the above can be true.
Answer: 1. Hint: Maybe picture yourself in San Diego: if you are facing south, which direction is the ocean?

Imagine you are looking down on the Earth from out in space. For a person standing at the place marked ``X'' north of the equator, what is the correct orientation of the directions?

Answer: 4. Hint: Maybe it helps to visualize looking at a globe: which direction would "W" be from this perspective? Or you could try and visualize yourself at the ``X''.

Imagine you are looking down on Earth's North Pole from out in space. For a person standing at the place marked ``X'', what is the correct orientation of the directions?

Answer: 4. Hint: This is almost the exact same orientation as in the previous question. ``N'' is the direction of the pole.

Imagine you are looking down on Earth's North Pole from out in space. For a person standing at the place marked ``X'', what is the correct orientations of the directions?

Answer: 1. Hint: Imagine yourself at the ``X''. If you are looking south, west will still be to your right.

Which direction does the person have to look to see the star shown below?

  1. North
  2. South
  3. East
  4. West
  5. None of the above
Answer: 1. Hint: Visualize the star's place on the dome - which compass direction is it closest to?

In what direction should you face to see this star when it is highest in the sky?

  1. Toward the north
  2. Toward the south
  3. Toward the east
  4. Toward the west
  5. Directly overhead
Answer: 2. Hint: The North Star shows you which direction is north, and the star gets highest on the dome opposite the North Star.


Rising and Setting

This is what the sky would look like at noon on a given day. Where would you expect the Sun to be located at sunset?

  1. On the horizon to the east.
  2. On the horizon to the west.
  3. On the horizon to the south.
  4. On the horizon to the north.
Answer: 2. Hint: "Rises in the east, sets in the west"

If you could see stars during the day, this is what the sky would look like at noon on a given day. The Sun is near the stars of the constellation Gemini. Near which constellation would you expect the Sun to be located at sunset?

  1. Leo
  2. Cancer
  3. Gemini
  4. Taurus
  5. Pisces
Answer: 3. Hint: "Rises in the east, sets in the west". Even though we often don't pay attention to them, the stars are doing almost the exact same thing as the Sun.

If you are standing at the North Pole, how would stars appear to move around the sky?

  1. Stars would rise in the east and set in the west.
  2. Stars would remain stationary in the sky.
  3. Stars would move in circles around the sky parallel to the horizon.
Answer: 3. Hint: Imagine standing at the North Pole in the diagram. All of the stars in the diagram circle around over your head.

If you are standing on the equator and looking east, stars will appear to move...

  1. from right to left (south to north).
  2. from left to right (north to south).
  3. straight up from the horizon.
  4. straight down toward the horizon.
Answer: 3. Hint: Try using the diagram above, and imagine standing on the black line with your head pointing away from the center of Earth. How would the stars appear to move?

If you look due north from San Diego, which picture shows how stars would move across the sky during a night? (Remember the North Star.)

Answer: 2. Hint: The North Star stands still in the sky. Stars still have to rise (or get higher in the sky) to the east, and set (or get lower in the sky) to the west.

Stars that never appear to set are called circumpolar. As you move from Earth's equator toward the North Pole, the number of stars that are circumpolar

  1. increases.
  2. decreases.
  3. stays the same.
Answer: 1. Hint: All stars are circumpolar at the North Pole, and none are at the equator.


Time of Day

For the person at position B, what direction would he have to look to see the Sun on the horizon?

  1. North
  2. South
  3. East
  4. West
Answer: 3. Hint: If that person is facing into the paper, he is looking south. Then would his left hand be east or west?

For the person at position B in the diagram above, roughly what time of day must it be?

  1. Noon
  2. 6 pm
  3. Midnight
  4. 6 am
Answer: 4. Hint: If the Sun is on the horizon in the east, it is sunrise, right?

Looking down on the Earth from above the North Pole, the Earth will

  1. rotate clockwise.
  2. rotate counterclockwise.
  3. not rotate clockwise or counterclockwise.
Answer: 2. Hint: "Rises in the east, sets in the west"

About what time of day would it appear to be for the person shown?

  1. 6 am
  2. 12 noon
  3. 6 pm
  4. 12 midnight
Answer: 3. Hint: "Rises in the east, sets in the west"

About what time of day would it appear to be for the person shown? ("NP" is the North Pole.)

  1. 2 pm
  2. 9 am
  3. 6 am
  4. 3 am
  5. 9 pm
Answer: 4. Hint: The person is on the night side of Earth. Remember that the person on the Earth will rotate counterclockwise from this point of view.


Seasons

On October 21st, which constellation is behind the Sun?

  1. Aries
  2. Virgo
  3. Libra
  4. Scorpius
  5. Pisces
  6. Taurus
Answer: 3. Hint: Find where Earth is in its orbit in October, and find the direction you need to look from Earth to see the Sun.

On November 21st, which constellation will be on the opposite side of the sky from the Sun?

  1. Aries
  2. Virgo
  3. Libra
  4. Scorpius
  5. Pisces
  6. Taurus
Answer: 6. Hint: Find where Earth is in its orbit in November, and look in the opposite direction from the Sun.

Which of the people shown would see the Sun as being highest overhead?

  1. Person 1
  2. Person 2
  3. Person 3
  4. Person 4
  5. Person 5
Answer: 3. Hint: "Overhead" is a direction pointing directly away from the center of the Earth.

In the diagram above, what season is it for person 1 in the northern hemisphere?

  1. Fall
  2. Summer
  3. Spring
  4. Winter
Answer: 4. Hint: He is in the northern hemisphere, which is tilted away from the Sun.

Which of the following statements about the location of the Sun at sunrise in the middle of winter is true?

  1. The Sun will rise north of east.
  2. The Sun will rise directly in the east.
  3. The Sun will rise south of east.
  4. None of the above.
Answer: 3. Hint: During winter, the northern hemisphere is tilted away from the Sun. which makes the Sun appear to go lower across the sky. This also means that we see less of the Sun's circle around the sky from our position on Earth.

As seen from your current location, when will an upright flagpole cast NO shadow (because the Sun is directly above the flagpole)?

  1. Every day at noon.
  2. Only on the first day of summer.
  3. Only on the first day of winter.
  4. On the first days of spring and fall.
  5. Never from your current location.
Answer: 5. Hint: In the United States, we are not close enough to the equator that the Sun can ever be overhead.

If the Sun is high in the sky to the southeast, what will the shadow of a stick be like?

  1. Short, pointing SE
  2. Short, pointing NE
  3. Short, pointing NW
  4. Short, pointing NE
  5. Long, pointing SE
  6. Long, pointing NE
  7. Long, pointing NW
  8. Long, pointing SW
Answer: 3. Hint: The shadow points exactly opposite the direction of the Sun. How long is your shadow at sunset? Noon?

Which of the people shown would collect more sunlight?

  1. Person A
  2. Person B
  3. Person C
  4. The collect the same amount because they are the same size.
Answer: 1. Hint: Look at which person is exposing the most body area to the sunlight coming from directly above.

If it is summertime right now, how does the altitude of the noontime Sun change (if at all) as winter approaches?

  1. It increases.
  2. It decreases.
  3. It stays the same.
Answer: 2. Hint: Remember which hemisphere (the northern or southern one) is tilted toward the Sun in summer and in winter.

The diagram below show possible ways of setting up Earth's orbit and Earth's rotation axis. In the two cases, would the Sun appear to change in size during a year?

  1. Hypothesis 1: no; Hypothesis 2: yes
  2. Hypothesis 1: no; Hypothesis 2: no
  3. Hypothesis 1: yes; Hypothesis 2: yes
  4. Hypothesis 1: yes; Hypothesis 2: no
Answer: 4. Hint: Think about how big an object appears to you if it is close or far away.

The diagram above show possible ways of setting up Earth's orbit and Earth's rotation axis. In the two cases, what season would it be in the souther hemisphere if it is summer in the northern hemisphere?

  1. Hypothesis 1: winter; Hypothesis 2: winter
  2. Hypothesis 1: winter; Hypothesis 2: summer
  3. Hypothesis 1: summer; Hypothesis 2: summer
  4. Hypothesis 1: summer; Hypothesis 2: winter
Answer: 4. Hint: How much of all of the Sun's light is falling in the two hemispheres?

Imagine the picture below shows the view of Earth from the Sun. To someone in the northern hemisphere, what would day and night be like?

  1. The Sun would be above the horizon for more than half of the day.
  2. The Sun would be above the horizon for less than half of the day.
  3. The Sun would be above the horizon for exactly half of the day.
Answer: 1. Hint: For a person in the north (especially at the North Pole) they stay on the lit side for more than half of a day.

Imagine the picture below shows two views of Earth from the Sun. To someone in the northern hemisphere, when would the Sun be higher in the sky at noontime?

  1. The noontime Sun would be higher in the sky for the day shown in picture A.
  2. The noontime Sun would be higher in the sky for the day shown in picture B.
  3. The noontime Sun would get equally high in the sky in both pictures.
Answer: 1. Hint: On Earth, the Sun is highest in the sky in the places that are facing most toward the Sun.

The pictures on the right side of the diagram below show views of the Earth from the Sun. Which one corresponds to summer in the southern hemisphere?

Answer: 3. Hint: Which one shows the southern hemisphere tilted toward the Sun.

If the Earth is oriented as shown in the diagram, are there places where it will be dark for more than 24 hours at a time?

  1. Yes - near the North Pole.
  2. Yes - on the Equator.
  3. Yes - on the side of the Earth facing away from the Sun.
  4. Yes - near the South Pole.
  5. No - everywhere will receive at least some sunlight.
Answer: 4. Hint: Draw in where the line between day and night would be. Even if the Earth is rotating, what part of Earth stays in the dark?

What would seasons be like on the planet shown below?

  1. There would be seasons, but the temperature changes would be more extreme than Earth's seasons.
  2. The seasons would be just like those on Earth.
  3. There would be seasons, but the temperature changes would be less noticeable than Earth's seasons.
  4. There would not be any seasons on this planet.
Answer: 1. Hint: As a planet orbits the Sun, its axis will always point in the same direction. This planet will have one of its hemispheres lit by the Sun for months at a time, but half a year later that same hemisphere will be in darkness for months at a time (and the other hemisphere would be lit).


Moon Phases

For more practice, see the Lunar Phase Quizzer animation.

The diagram below shows Earth and the Sun as well as 5 different possible positions of the Moon. Which position of the Moon best corresponds with the phase of the Moon shown in the box?

Answer: 4. Hint: The Moon's phases are caused by its own shadow, not the Earth's shadow. At position 5, the Moon would also be crescent, but with the lit portion on the right.

How much of the Moon's entire surface is illuminated by the Sun during the phase shown in the box above?

  1. None of the surface is illuminated.
  2. Less than half of the surface is illuminated.
  3. Half of the surface is illuminated.
  4. More than half of the surface is illuminated.
  5. All of the surface is illuminated.
Answer: 3. Hint: We are only seeing part of illuminated side of the Moon, but it is still there...

How much of the Moon's illuminated surface is visible from Earth during the phase shown in the box above?

  1. None of the surface (visible from Earth) is illuminated.
  2. Less than half of the surface (visible from Earth) is illuminated.
  3. Half of the surface (visible from Earth) is illuminated.
  4. More than half of the surface (visible from Earth) is illuminated.
  5. All of the surface (visible from Earth) is illuminated.
Answer: 2. Hint: Most of the lit side is facing away from us (and is on the side of the Moon facing away from us).

The diagram below shows Earth and the Sun as well as 5 different possible positions of the Moon. Which position of the Moon best corresponds with the phase of the Moon shown in the box?

Answer: 2. Hint: At position 1 or 2, the Moon will appear more than half lit. At position 1, the Moon would have the dark portion on the left. You can try this out with a tennis ball and a strong light bulb (your head plays the role of Earth.)

How much of the Moon's illuminated surface is visible from Earth during the phase shown in the box above?

  1. None of the surface (visible from Earth) is illuminated.
  2. Less than half of the surface (visible from Earth) is illuminated.
  3. Half of the surface (visible from Earth) is illuminated.
  4. More than half of the surface (visible from Earth) is illuminated.
  5. All of the surface (visible from Earth) is illuminated.
Answer: 4. Hint: In this case, most of the lit side is on the side of the Moon facing toward us.

What does the Moon's phase look like from the northern hemisphere of Earth (the part of Earth facing you in the figure below)?

Answer: 2. Hint: Can you see more than half of the lit side from Earth?

What would the Moon's phase look like from the northern hemisphere of Earth (the part of Earth facing you in the figure below)?

Answer: 4. Hint: Look at the diagram upside-down (like your point of view on the side of Earth facing the Moon).

For a person on Earth, at what time would the Moon be highest overhead when the Moon is at the position shown?

  1. Noon
  2. 6 pm
  3. Midnight
  4. 6 am
  5. None of the above
Answer: 3. Hint: You have to be in the middle of the nighttime side of Earth for you head to be pointing at the Moon.

If the Moon is positioned as shown below, about what time would it be overhead?

  1. 9 am
  2. 3 pm
  3. 9 pm
  4. 3 am
  5. None of the above
Answer: 4. Hint: You would have to be standing in lower left part of Earth for your head to be pointing toward the Moon. According to the way the Earth is rotating, that would be between midnight and sunrise (6 am).

If the Moon is positioned in its orbit as shown below, at what time would it be highest overhead?

  1. 9 am
  2. 3 pm
  3. 9 pm
  4. 3 am
  5. None of the above
Answer: 2. Hint: You have to be on the upper right portion of Earth to see the Moon nearly overhead, which puts you on the lit side of Earth, past noon. This is just like earlier questions about when constellations rise and set.

If the Moon is positioned as shown below, about what time would the Moon rise?

  1. Sunset
  2. Midnight
  3. Sunrise
  4. Noon
  5. None of the above
Answer: 2. Hint: The Moon is highest overhead at sunrise (person standing at the bottom of Earth), so the Moon would rise about 6 hours earlier.

If the Moon is positioned as shown below, about what time would the Moon set?

  1. 9 pm
  2. 3 am
  3. 9 am
  4. 3 pm
  5. None of the above
Answer: 1. Hint: The Moon would be overhead at about 3 pm (person standing at upper right part of Earth), so the Moon would set about 6 hours later.

What is the phase of the Moon when it is in the position shown above?

  1. waxing crescent
  2. waxing gibbous
  3. waning gibbous
  4. waning crescent
Answer: 1. Hint: You would see less than half of the lit side from Earth, and since the Moon orbits counterclockwise from the point of view of the picture, it must be waning (appearing to get more full).

Which phase of the Moon rises in the east as the Sun rises in the east?

  1. first quarter
  2. full
  3. third quarter
  4. new
Answer: 4. Hint: If it rises at the same time as the Sun, the Sun must be on the opposite side of the Moon from us.

What would the Moon's phase look like if it was in the position shown?

Answer: First row on the right. Hint: The Moon has to be a crescent, roughly midway in phase between third quarter and new. Try figuring out where the Moon has to be for us to see the other phases shown.

Many people incorrectly believe that Earth's shadow causes Moon phases. If this incorrect belief were true, then which location would produce the Moon phases shown in the upper right corner of the figure below?

Answer: 2. Hint: The Moon would only go into the Earth's shadow when it is on the opposite side of the Earth from the Sun. Typically though we see new Moon when it is at position 4, and we are looking at the Moon's shadowed side.


Eclipses

If we make the Earth the size of a basketball (12 in. across), then if the Moon is also made the same scale, it should be about 3 in. across. How far from Earth should the Moon be on this scale?

  1. 2 inches away
  2. 1 foot away
  3. 4 feet away
  4. 30 feet away
  5. 300 feet away
Answer: 4. Hint: The distance between them is about 30 times the size of the Earth... far out (literally)!

What does the Moon's phase have to be if there is a solar eclipse?

  1. new
  2. first quarter
  3. full
  4. third quarter
  5. It can happen in any phase.
Answer: 1. Hint: How do the Earth, Sun, and Moon have to be oriented?

What phase does the Moon have to be for there to be a lunar eclipse?

  1. new
  2. first quarter
  3. full
  4. third quarter
Answer: 3. Hint: How do the Earth, Sun, and Moon have to be oriented?

At what times is it possible to see a lunar eclipse from Earth?

  1. Any time during nighttime.
  2. Any time during daytime.
  3. Only at midnight.
  4. Only at noon.
  5. Only at sunrise.
  6. Only at sunset.
Answer: 1. Hint: When a lunar eclipse is occuring, anyone on the nighttime side of Earth could potentially see it.

Match the appearance of the solar eclipse (the numbered choices) with the place you would have to be to see it (the letters) in the figure below.

Answer: A: 4. B: 2. C: 1. D: 3. Hint: How do the dashed lines help tell you whether you can see the top or bottom edges of the Sun?

What would the Moon look like (from Earth) when it is at the positions (A and B) shown?

An observer on Earth sees a total lunar eclipse. At the same time, if someone is standing on the Moon facing the Earth, what would they see?

  1. Earth's night side, not eclipsing the Sun
  2. Earth's day side, not eclipsing the Sun
  3. Earth partially eclipsing the Sun
  4. Earth totally eclipsing the Sun
Answer: 4. Hint: A total eclipse on the Moon means that no sunlight is reaching it.


Planet Motions in the Sky

If you carefully watch over several nights, how will the Moon apear to move compared to stars in constellations?

  1. From east to west.
  2. From west to east.
  3. The Moon doesn't appear to move over several nights.
Answer: 2. Hint: This is different than rising and setting! If you can forget about the Earth's rotation as the Moon moves around the Earth, it goes counterclockwise around the diagram and would be in front of different stars over time.

Where would you look to see a planet rise when it is in retrograde motion?

  1. Near the eastern horizon.
  2. Near the western horizon.
Answer: 1. Hint: Everything rises in the eastern half of the sky, and set in the western half because of Earth's rotation. The retrograde motion doesn't matter here.

A planet moving in retrograde motion will, over the course of one night, appear to

  1. move east to west.
  2. move west to east.
  3. not move at all, as planets do not move with the stars.
  4. move randomly, as planets move differently than the stars.
Answer: 1. Hint: The Earth's rotation is much quicker than the planet's motion through the sky, and the rotation is what makes things rise in the east and set in the west.

A planet is moving in retrograde motion. Over the course of several nights, how will the planet appear to move relative to the background stars?

  1. move east to west.
  2. move west to east.
  3. It will not move at all, as planets do not move with the stars.
  4. It will move randomly, as planets move differently than the stars.
Answer: 1. Hint: Relative to the stars, a planet normally moves from west to east. Retrograde motion (relative to the stars) is in the opposite direction.

If Venus and the Sun are on separate merry-go-rounds, but both are making one circle of the Earth in exactly the same amount of time, what would we see from Earth over time?

  1. Venus would at first appear to move closer to the Sun.
  2. Venus and the Sun would move together, always in the same positions relative to each other.
  3. Venus would at first appear to move farther away from the Sun.
  4. Venus would stay near the Sun, but would appear to circle around it.
Answer: 2. Hint: If the two merry-go-rounds circle in the same amount of time, it is just as if the two merry-go-rounds were attached.

If Venus and the Sun are on separate merry-go-rounds (as pictured in the previous question), but Venus' merry-go-round makes one circle of the Earth in slightly less time than the Sun's merry-go-round does, what would we see from Earth over time?

  1. Venus would at first appear to move closer to the Sun.
  2. Venus and the Sun would move together, always in the same positions relative to each other.
  3. Venus would at first appear to move farther away from the Sun.
  4. Venus would stay near the Sun, but would appear to circle around it.
Answer: 1. Hint: Venus' merry-go-round is moving faster in this case, so it would catch up with the Sun.

In the heliocentric model shown below, where would a planet have to be to be seen overhead by a person at midnight on Earth?

Answer: 7. Hint: To see something as being high overhead, you have to be looking away from the center of the Earth. Where would a person have to be standing for it to be midnight on Earth?

In the picture above, at roughly what time would the planet at position 5 be roughly overhead (high above the horizon)? (Earth rotates counterclockwise from this point of view.)

  1. 3 am.
  2. 9 am.
  3. 3 pm.
  4. 9 pm.
  5. It is not possible to tell from the diagram.
Answer: 2. Hint: A person would have to be on the lit side of the Earth in the lower right for the planet to be overhead.

The picture shows the solar system today. Which planet will be highest overhead at around midnight?

  1. Jupiter (J)
  2. Mars (M)
  3. Pluto (P)
  4. Saturn (S)
  5. Uranus (U)
Answer: 5. Hint: This is the only planet on the opposite side of Earth from the Sun. (To see Saturn , you would have to look in the same direction as the Sun...)

The picture shows the inner solar system today. When would Venus (V) be highest overhead? (Earth rotates counterclockwise in this view.)

  1. Late morning (6 am - noon)
  2. Afternoon (Noon - 6 pm)
  3. Evening (6 pm - midnight)
  4. Early morning (Midnight - 6 am)
Answer: 1 Hint: You have to be on the daytime side of Earth (the side facing the Sun) in the morning (the Earth would have recently rotated you off the nighttime side of Earth.)

If you lived on Venus and you monitored Earth's position in the sky over the course of several years, what would you see?

  1. Earth always moves from east to west relative to the stars.
  2. Earth always moves from west to east relative to the stars.
  3. Earth usually move from west to east relative to the stars, but would occasionally undergo retrograde motion (east to west).
  4. Earth is always fairly close to the Sun in the sky, and is most easily visible before sunrise or after sunset.
Answer: 3. Hint: From the point of view of someone on Venus, Earth is a superior planet (it has a larger orbit than Venus). Thus, it will act in the same way that Mars acts when we view it from Earth.

If you lived on another planet and you watched Earth's position in the constellation sover the course of several years, which ones would see Earth do retrograde motion? (Give all correct answers.)

  1. Mercury
  2. Venus
  3. Mars
  4. Jupiter
  5. Saturn
Answer: 1,2. Hint: From the point of view of someone on Mercury or Venus, Earth is a superior planet (has a larger orbit), and will do retrograde motion on occasion.


Kepler's Laws

NASA wants to launch a spaceship from Earth (inner circle) to Mars (outer circle) and immediately come back. Which of the pictured orbits is possible according to Kepler's first law?

Answer: 1. Hint: If the orbit is any kind of oval, the Sun will NOT be at the center of the oval.

Mars moves in an elliptical orbit around the Sun. The location of the Sun relative to this ellipse is

  1. at the focus which is closer to the point where Mars is moving the slowest.
  2. at the focus which is closer to the point where Mars is moving the fastest.
  3. at the center of the ellipse.
  4. at one end of the longer axis of the ellipse.
  5. at one end of the shorter axis of the ellipse.
Answer: 2. Hint: Think about Kepler's First Law of planetary motion.

The picture below shows the orbit of a planet around the Sun with the planet in different positions. Rank the planet's speed when it is at the different positions in order from fastest to slowest.

  1. Z > V > Y > W > X
  2. X > W > Y > V > Z
  3. Z > Y > X > W > V
  4. X > Y > Z > V > W
  5. V > W > X > Y > Z
Answer: 1. Hint: Think about Kepler's Second Law of planetary motion.

The Earth is a few percent closer to the Sun in January than it is in July. What does this fact mean for the lengths of the seasons?

  1. Winter in the northern hemisphere will be a few days longer than summer.
  2. Summer in the northern hemisphere will be a few days longer than winter.
  3. This does not change the fact that the seasons are all of equal length.
Answer: 2. Hint: Think about Kepler's Second Law of planetary motion. Is the Earth moving faster around its orbit in January or July?

If a small weather satellite and the large International Space Station are orbiting Earth at the same altitude above Earth's surface, which object takes longer to orbit once around Earth?

  1. The large space station.
  2. The small weather satellite
  3. They would take the same amount of time.
Answer: 3. Hint: Kepler's Third Law says that the time it takes an object to orbit (its period) only depends on its distance from the object it is orbiting.

NASA wants to launch a spacecraft to go out to the planet Mars (without stopping there), and then come back. If the spacecraft never uses rockets after it leaves Earth, how long will it take the satellite to make its orbit?

  1. The spacecraft will make one complete orbit in a year.
  2. The spacecraft will take less than one year to make a complete orbit.
  3. The spacecraft will take more than one year to make a complete orbit.
Answer: 3. Hint: Think about Kepler's Third Law of planetary motion.

How long will it take the spacecraft to make a complete orbit around the Sun compared to the time it takes Mars to complete an orbit?

  1. The spacecraft will make one complete orbit in the same amount of time it takes Mars to make a complete orbit.
  2. The spacecraft will take less time to make a complete orbit than it takes Mars.
  3. The spacecraft will take more time to make a complete orbit than it takes Mars.
Answer: 2. Hint: Think about Kepler's Third Law of planetary motion.

A newly discovered asteroid is observed orbiting the Sun at an average distance of 4 astronomical units (AU). How long will it take to orbit the Sun?

  1. 2.3 years
  2. 4 years
  3. 8 years
  4. 16 years
  5. 64 years
Answer: 3. Hint: Use Kepler's Third Law of planetary motion.


Models of the Universe

The figure below shows a portion of Ptolemy's model of the universe. What phases would you see for Venus when it is at the positions given by letters if you are using a telescope on Earth?

The figure below shows a portion of Copernicus' model of the universe. If Venus was in the positions given by letters, what phases would you see through a telescope from Earth?


Motion and Newton's Laws

A car is sitting still on a road. The car's

  1. velocity and acceleration are zero.
  2. velocity is not zero but its acceleration is zero.
  3. acceleration is not zero, but its velocity is zero.
  4. velocity and acceleration are both not zero.
Answer: 1. Hint: If the car is not moving and staying that way, both will be zero.

A car is travelling along a straight, flat road at constant speed. The car's

  1. velocity and acceleration are zero.
  2. velocity is not zero but its acceleration is zero.
  3. acceleration is not zero, but its velocity is zero.
  4. velocity and acceleration are both not zero.
Answer: 2. Hint: The car is moving, but the velocity is not changing (neither speed nor direction.

A car is travelling at constant speed around a curve. The car's

  1. velocity and acceleration are zero.
  2. velocity is not zero but its acceleration is zero.
  3. acceleration is not zero, but its velocity is zero.
  4. velocity and acceleration are both not zero.
Answer: 4. Hint: The direction of the car's velocity is changing.

Beaker is riding on a cart and is not wearing a seatbelt. The chair hits a wall and stops. What is the best description of what happens to Beaker?

  1. Beaker's body keeps moving forward until he hits the wall.
  2. Beaker stops at the same instant the cart does.
  3. Beaker pops up at the instant the car hits the wall.
Answer: 1. Hint: Newton's First Law... he keeps moving in a straight line at constant speed.

Is there a net (unbalanced) force acting in the following situations?

  1. A car is coming to a stop
  2. A bus is speeding up.
  3. An elevator moves upward at constant speed.
  4. A bicycle goes around a curve.
  5. A moon orbits Jupiter.
Answers: 1: Yes; 2: Yes; 3: No; 4: Yes; 5: Yes. Hint: If an object is accelerating, there must be an unbalanced force.

The pictures below show boxes (that are initially at rest) and the forces that are acting on them. In each case, what is going to happen to the box?

  1. The box will move to the left.
  2. The box will move to the right.
  3. The box will move upward.
  4. The box will move downward.
  5. The box will not move.
Answer: A: 1. B: 3. C: 5. D: 2. Hint: Newton's First Law - the box will move in the direction of the net force.

Which of the following diagrams best represents the forces acting on a ball hanging from a string?

Answer: 3. Hint: Newton's First Law - the ball is not moving, so there can be no net force. Gravity is pulling down, and the string exerts a force pulling upward.

Which of the following diagrams best represents the forces acting on a cart sitting still on a table?

Answer: 3. Hint: Newton's First Law - the cart is not moving, so there can be no net force. Gravity is pulling down, and the table exerts a force pushing upward from below.

You are late for class and driving too fast when you enter into a sharp right turn. The tires lose their grip on the road. What is probably going to end up happening?

  1. The car will skid to the right of the direction it was going at the time of the skid.
  2. The car will skid in a straight line in the direction that it was going at the time of the skid.
  3. The car will skid to the left of the direction it was going at the time of the skid.
Answer: 2. Hint: Newton's First Law - friction with the road is need to keep the car in the turn.

A ball is rolling in a straight line as shown in the figure below (from the view of someone standing over the table). If it is struck on the left side, what is going to happen to its motion?

  1. It will speed up, but will continue moving in the same direction.
  2. It will slow down, but will continue moving in the same direction.
  3. It will immediately start moving directly to the right.
  4. It will immediately start moving directly to the left.
  5. It will move in a straight line, but somewhat to the right of its original direction.
  6. It will move in a straight line, but somewhat to the left of its original direction.
  7. It will continue moving in the same direction at the same speed.
Answer: 5. Hint: The acceleration of the ball is in the same direction as the force points.


I am swinging a ball on a string counterclockwise around my head (as seen from above in the picture below). At the instant shown, In which direction is the ball's velocity pointing?

  1. Toward me.
  2. Away from me.
  3. To the left.
  4. To the right.
Answer: 3. Hint: At the instant shown, the ball is moving from right to left across the top of the circle.

At the same instant, in which direction is there a net force acting?

  1. Toward me.
  2. Away from me.
  3. To the left.
  4. To the right.
Answer: 1. Hint: The ball has has gotten as far toward the top of the diagram as it is going to get, so I must be pulling toward the bottom of the diagram.

I swing a ball on a string counterclockwise above my head (as seen from above in the picture below). At the point shown, I suddenly release the string. Which of the paths below would the ball most closely follow when released?

Answer: 2. Hint: Newton's First Law - once the net force (the pull on the string) is gone, the ball will travel in a straight line in the direction it was travelling.


I roll a marble around a circular track that has a section cut out. When the marble reaches the end of the track, what path will it take?

Answer: B. Hint: Newton's First Law - once the net force (exerted by the track) is gone, the marble will travel in a straight line in the direction it was travelling.

The space shuttle fires its engine. What forces act on the space shuttle?

  1. Two forces: one from the exhaust gas, and the equal and opposite force.
  2. One force from the exhaust gas.
  3. There is no force acting because they cancel out.
Answer: 2. Hint: There is a second force acting on the gas. That is what Newton's Third Law is referring to.

A red cart is going to hit a pair of blue carts with a spring-loaded pusher. (The pair of blue carts has twice the mass of the red cart.) After the hit, which cart will have accelerated (sped up) more?

  1. The red cart.
  2. The pair of blue carts.
  3. Both experience the same acceleration.
Answer: 1. Hint: Newton's Third Law tells you about the forces on the red and blue carts, but you also need to consider Newton's second law to determine the effect of the forces.

Suppose you are an astronaut taking a space walk to fix your spacecraft with a hammer. Your tether line breaks and the jets on your backpack are out of fuel. How could you return to your spacecraft without the help of someone else?

  1. throw the hammer at the ship
  2. throw the hammer away from the ship
  3. flap your arms
  4. kiss your ship good-bye
Answer: 2. Hint: Newton's Third Law.

An asteroid is moving through space at constant velocity. At the time shown, a rocket that is attached to the asteroid starts to fire continuously toward the bottom of the screen. Which of the paths would the asteroid most closely follow as the rocket fires?

Answer: C. Hint: Newton's Third Law tells you about that gas being shot downward will exert a force upward on the rocket and asteroid. If the rocket is firing continuously, then it will cause the asteroid to move on a curved path because the force continues to accelerate the asteroid upward.

A compact car and a large truck collide head-on and stick together. Which vehicle exerts the largest force during the collision?

  1. The car.
  2. The truck.
  3. Both exert the same force.
  4. Neither exerts a force on the other - the car gets smashed simply because it gets in the way of the truck.
Answer: 3. Hint: Newton's Third Law.

A compact car and a large truck collide head-on and stick together. Which vehicle undergoes the largest acceleration during the collision?

  1. The car.
  2. The truck.
  3. Both experience the same acceleration.
  4. You can't tell without knowing how fast the vehicles were moving before the collision.
Answer: 1. Hint: Newton's Second Law tells you about the amount of acceleration for objects with different masses. The forces on the two vehicles are the same (see previous question).

If the planet is moving with the velocity shown in blue, what will the Sun's gravitational force (red) be doing to the planet at the point shown?

  1. Speeding it up
  2. Slowing it down
  3. Keeping same speed
  1. Turning it to your left
  2. Turning it to your right
  3. Keeping same direction
Answer: Part a: 1., Part b: 2. Hint: The direction of the force tells the story: it is pulling in roughly the same direction the planet is moving (causing it to speed up), and is pulling somewhat toward the right hand side (making the planet start turning that way). This could make it go around the orbit shown below.


Gravity

A hypothetical planet system has planets in equally-spaced circular orbits. The planet masses are given in terms of the mass of the innermost planet. Which of the planets exerts the greatest gravitational force on the star?

Answer: B. Hint: Compare to the strength of planet D's force. Planet A is 16x more massive, but 4 times further away, so those factors cancel - its force is the same as planet D. Planet C will exert a smaller force than D - the distance reduces the force more than the larger mass increases it. Planet B has a large enough mass that its force is larger than planet D's force (10/9ths, to be exact.)

You and your friend measure the strength of the force of gravity acting on both of you when you are on the surface of Earth. Your friend has 3 times as much mass as you do. The force on your friend is

  1. 1/3 as large
  2. 1/9 as large
  3. 3 times as large
  4. 9 times as large
  5. the same
as the force on you.

Answer: 3. Hint: Gravitational force is stronger the more mass is involved: 3 times stronger if there is 3 times more mass in one of the objects.

An astronaut measures the strength of the force of gravity acting on him when he is on the surface of Earth and when he is 10 times farther away from the center of Earth. How do they compare?

  1. When he is farther away, the force is 1/10th as large.
  2. When he is farther away, the force is 1/100th as large
  3. When he is farther away, the force is 1/1000th as large.
  4. When he is farther away, the force is 10 times larger.
  5. When he is farther away, the force is 100 times larger.
  6. When he is farther away, the force is 1000 times larger.
Answer: 2. Hint: Gravitational force decreases with distance, and it decreases as the square of the distance.

A person measures the strength of the force of gravity acting on him when he is on the surface of Earth, and compares it to the force acting on his friend (who is twice as massive) when his friend is 10 times farther away from the center of Earth. How do they compare?

  1. The force on his friend is 1/5th as large.
  2. The force on his friend is 1/10th as large
  3. The force on his friend is 1/25th as large.
  4. The force on his friend is 1/50th as large.
  5. The force on his friend is 1/100th as large.
Answer: 4. Hint: As in the previous question, the (10 times) larger distance would reduce the force to 1/100th of the force on him, but his friend's larger mass makes the force twice as large as it would have been if they were the same mass.

An astronaut goes on the first mission to Mars. Mars has a mass that is only about one-tenth the mass of the Earth, and it is about half the size of Earth (so that she is closer to the center of the planet when she is standing on the surface). How will her weight on Mars compare to her weight on Earth?

  1. Same as her weight on Earth.
  2. 1/2 (50%) of her weight on Earth
  3. 2/5 (40%) of her weight on Earth
  4. 1/4 (25%) of her weight on Earth
  5. 1/5 (20%) of her weight on Earth
  6. 1/10 (10%) of her weight on Earth
Answer: 3. Hint: Because Mars has a smaller mass, there is less gravitational force (1/10th as large as Earth because of that alone). However, because Mars is smaller than Earth, a person on the surface is closer to all of the mass of Mars, which makes the gravitational force larger (4 times larger than it would be otherwise).

Consider a person standing in an elevator that is accelerating upward. The upward force exerted by the elevator floor on the person is

  1. larger than
  2. identical to
  3. smaller than

the downward weight of the person.

Answer: 1. Hint: Gravity (the weight) is pulling down. To have a net force (and thus, to accelerate the person) upward, the floor must exert a force on the person that is larger than gravity.

Load and fire a cannonball with a speed of 6 km/s in the animation here. What will happen if we increase the speed of the cannonball to 8 km/s?

  1. The cannonball will go flying away from Earth.
  2. The cannonball will orbit Earth.
  3. The cannonball will go more than half way around Earth before crashing to the ground.
Answer: 2. Hint: For 6 km/s the cannonball gets close to half way around the Earth before crashing. A little extra upsh will get the cannonball into a circular orbit. Once the cannonball is able to get halfway around Earth, it will be able to get the rest of the way around --- the lowest point of its orbit will miss Earth's surface. For slower cannonballs, the lowest point in the orbit is inside the Earth - CRASH!

A spacecraft hovers near a small asteroid (with the help of its rocket) as they are both moving toward the right. Which of the paths would the asteroid most closely follow as time goes on?

Answer: E. Hint: The spacecraft will exert a downward pull on the asteroid (in the diagram) that will slowly start to accelerate the asteroid downward.


Some of the questions above are taken from the following sources:

J. P. Adams, D. J. Loranz, E. E. Prather, and T. F. Slater. Lecture Tutorials for Introductory Astronomy -- Instructor's Guide, 2002 (Prentice Hall).

E. Mazur. Peer Instruction: A User's Manual, 1997 (Prentice Hall).


Last update: February 20, 2013