PHYS 107 ASTRONOMY 3

• Question 1

  1 out of 1 points

  	If the radius of the Earth were to double (with all other things unchanged), the force of gravity it would feel from the Sun would be:
  	Selected Answer:   be unchanged Correct Answer:  be unchanged Response Feedback: Correct, since the distance between the centers of the Earth and Sun does not change the force of gravity does not change between them.

• Question 2

  1 out of 1 points

  	Kepler's second law, the law of equal areas, implies that:
  	Selected Answer:   planets move faster when they are closer to the Sun Correct Answer:  planets move faster when they are closer to the Sun Response Feedback: Correct, since the Sun lies "off-center" (at one focus of the orbit), for the line connecting the planet and Sun to sweep out the same area in the same time the planet must move faster when it is closer to the Sun.

• Question 3

  1 out of 1 points

  	You have two spacecraft (the Enterprise and Constellation) that are identical except for the force that their rocket motors can generate.  If the Enterprise spacecraft can generate a force twice as great as the Constellation, its acceleration will be (______________) as great as the Constellation's acceleration.
  	Selected Answer:   2 times Correct Answer:  2 times Response Feedback: Correct, if the spacecraft are identical except for the force generated this means their masses must be the same.  Since: Force = mass times acceleration then if the force is doubled the acceleration will be doubled (Newton's 2nd Law).

• Question 4

  1 out of 1 points

  	Calico Kaylee the space kitten has a mass of 0.5 kg and a weight of 1.1 pounds.  If she is launched on a trip to the Moon, during the trip her mass:
  	Selected Answer:   is always unchanged Correct Answer:  is always unchanged Response Feedback: Correct, her mass is unchanged throughout the trip, however her weight will change as she will experience different gravitational accelerations (due to the variation is distances from the Earth and Moon) throughout her trip.

• Question 5

  1 out of 1 points

  	If the Sun were to suddenly expand to be 10 times its current size of ~0.0047 AU but keep the same mass, the Earth would:
  	Selected Answer:   stay in the same orbit Correct Answer:  stay in the same orbit Response Feedback: Correct, the force on the Earth would be unchanged since the mass of the Sun is unchanged, so the orbit would not change. Note this would not be true if the Sun were to expand to be larger than the Earth's orbit of course. Also note that orbital distances are defined from both object's centers, so while the Earth in some sense is "closer" to the Sun's surface, its distance from the Sun's center and hence its orbital distance is unchanged.

• Question 6

  1 out of 1 points

  	The velocity vector of a planet in orbit points:
  	Selected Answer:   tangentially to the orbit (at 90 degrees to the line connecting the star and planet) in the direction of motion Correct Answer:  tangentially to the orbit (at 90 degrees to the line connecting the star and planet) in the direction of motion Response Feedback: Correct, look again at the web simulator and click on the velocity vector.

• Question 7

  1 out of 1 points

  	You are an astronaut sent up to repair the Hubble Space Telescope and you lose your grip on the space shuttle and begin to float away carrying your tool kit.  In order to get back to the space shuttle you should:
  	Selected Answer:   throw your tool kit in the direction opposite to the space shuttle Correct Answer:  throw your tool kit in the direction opposite to the space shuttle Response Feedback: Correct, remember Newton's 3rd law, since for every action their is an equal an opposite reaction, when you throw the tool kit away from the shuttle you will experience a force toward the shuttle.

• Question 8

  1 out of 1 points

  	The force on the Moon from the Earth is ( ) to the force on the Earth from the Moon.
  	Selected Answer:   exactly equal to Correct Answer:  exactly equal to Response Feedback: Correct, notice gravity obeys Newton's laws so it is symmetric, the force (but not acceleration) is always equal.

• Question 9

  0 out of 1 points

  	The mass of Jupiter can best be calculated by
  	Selected Answer:    knowing the Sun's mass and measuring how Jupiter's speed changes during its elliptical orbit around the Sun. Correct Answer:    measuring the orbital period and distance of one of Jupiter's moons. Response Feedback:  Incorrect, the motions of bodies around Jupiter can best be used to determine the mass of Jupiter

• Question 10

  1 out of 1 points

  	How did the Ptolemaic model explain the apparent retrograde motion of the planets?
  	Selected Answer:    The planets moved along small circles that moved on larger circles around the Earth. Correct Answer:    The planets moved along small circles that moved on larger circles around the Earth. Response Feedback:  Correct, the Ptolemaic model used multiple circles called deferents to explain the observed orbits of the planets

• Question 11

  1 out of 1 points

  	Which of the following would cause the force on the Moon by Earth to increase by the largest amount?
  	Selected Answer:   move the moon two times closer to Earth Correct Answer:  move the moon two times closer to Earth Response Feedback: Correct, since the force of gravity depends on one over the distance squared, decreasing the distance by a factor of 2 increases the force of gravity by a factor of 4 (Newton's Law of Universal Gravitation). Note that doubling either mass is equivalent, and both result in increasing the force on both the Moon and Earth by a factor of 2. Doubling the orbital radius would decrease the force by a factor of 4 (Newton's Law of Universal Gravitation). How does this compare to your answer to #3 on page 30 of lecture-tutorials?

• Question 12

  1 out of 1 points

  	The Sun suddenly collapses into a black hole of the same mass, what would happen to the Earth and other planets?
  	Selected Answer:   they would continue in their current orbits Correct Answer:  they would continue in their current orbits Response Feedback: Correct, the mass is the same so nothing in Newton's Law of Universal gravitation changes so the orbits would be unchanged.

• Question 13

  1 out of 1 points

  	Galileo challenged the idea that objects in the heavens were perfect by:
  	Selected Answer:    observing sunspots on the Sun and mountains on the Moon Correct Answer:    observing sunspots on the Sun and mountains on the Moon Response Feedback:  Correct, although they did not satisfy Cardinal Bellermine

• Question 14

  0 out of 1 points

  	Given Kepler's 3rd Law (P2=a3), if we were to assume circular orbits so that the speed of a planet was constant around the Sun, what relation would exist between the speed of a planet and its semi-major axis?
  	Selected Answer:   v=2 π √ a Correct Answer:  v=2 π /√ a Response Feedback: Incorrect, the circumference of a circular orbit is  2 π a, and the period is  P =a * √ a, so since the speed is distance divided by time it equals  v=2 π /√ a.

• Question 15

  1 out of 1 points

  	If after class you climb from this room to the top of the Natural Sciences building your weight will be:
  	Selected Answer:   a tiny amount less Correct Answer:  a tiny amount less Response Feedback: Correct, since your distance from the center of the Earth will be just slightly larger, so the force of gravity upon you will be a tiny bit less and thus your weight will be just a tiny bit lower.

• Question 16

  1 out of 1 points

  	If the radius of the Earth were to double (all other things being equal) your weight would:
  	Selected Answer:   decrease by a factor of 4 Correct Answer:  decrease by a factor of 4 Response Feedback: Correct, since the distance between the centers of the Earth and you changes by a factor of 2 the force of gravity and thus your weight (the force of gravity upon you) must change, if the radius doubles by Newton's Law of Universal Gravitation the force will change by a factor of 1/r^2 or decrease by a factor of 4.

• Question 17

  0 out of 1 points

  	Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet's year (orbital period) compare to Earth's year?
  	Selected Answer:    The planet's year would be the same as Earth's. Correct Answer:    The planet's year would be shorter than Earth's. Response Feedback:  Incorrect, since the period depends on the inverse of the mass as well as the semi-major axis

• Question 18

  1 out of 1 points

  	If astronomers detect an asteroid which orbits the Sun with an orbit that has an eccentricity of 0.5 and a semi-major axis of 1 AU what is its orbital period?
  	Selected Answer:   1 year Correct Answer:  1 year Response Feedback: Correct, since the semi-major axis is the same as the Earth's the asteroid will orbit with the same period as the Earth, namely 1 year.

• Question 19

  1 out of 1 points

  	Imagine a new planet in our solar system with an orbital period of 5 years, what approximately is its distance from the Sun?
  	Selected Answer:   3 AU Correct Answer:  3 AU Response Feedback: Correct, as 3 cubed is 27 and the square-root of 27 is approximately 5 so by Kepler's Third Law the period will be approximately 5 years.

• Question 20

  1 out of 1 points

  	The fact that Voyager 10 continues to speed out of the solar system, even though its rockets have no fuel, is an example of:
  	Selected Answer:    Newton's first law of motion. Correct Answer:    Newton's first law of motion. Response Feedback:  Correct, the first law says that a body in motion will stay in uniform motion unless acted upon by an external force