Astronomy 122&, Fall 2009

Homework B: Due Monday, September 14

Part I: Multiple choice. On your scantron fill out your NAME, STUDENT NUMBER, and NETWORK ID both in writing and in the bubbles. In addition, fill out "FORM B."

1. "Velocity" implies both
a) mass and direction
b) speed and direction
c) speed only
d) direction and momentum
e) speed and momentum

2. If you were to triple the mass of the Earth but keep the radius the same you would weigh
a) the same as you do now
b) 3 times as much as you do now
c) 1/3 as much as you do now
d) 9 times as much as you do now
e) 1/9 times as much as you do now

3. If you were to triple the radius of the Earth but keep the mass the same you would weigh
a) the same as you do now
b) 3 times as much as you do now
c) 1/3 as much as you do now
d) 9 times as much as you do now
e) 1/9 as much as you do now

4. Where does the Earth's gravity actually end?
a) at the Sun
b) at the end of the planetary system
c) at the nearest star
d) at the Moon
e) nowhere

5. As you descend in an elevator in a tall building at constant speed, your weight
a) decreases
b) increases
c) stays the same.
d) does something, but you can't predict what
e) depends on the elevator's speed in meters per second

6. Orbiting astronauts are weightless because the
a) shuttle is out of the Earth's gravity.
b) cabin's hull shields the astronauts from the Earth's gravity.
c) Earth's gravity is balanced by the Moon's gravity
d) Earth's gravity is balanced by the Sun's gravity
e) astronauts and the cabin are both free-falling bodies.

7. If you could cut off the gravity of the Sun and planets (which you cannot), Mars would
a) go into a perfectly circular orbit around the Sun
b) go flying away from the Solar System in a straight line
c) go into an elliptical orbit relative to the Sun
d) rotate faster
e) fall directly into the Sun

8. What is at one focus of the orbit of a planet?
a) the planet
b) Ursa Major
c) Polaris
d) the Sun
e) nothing; both foci are empty

9. For the Solar System, the period of a planet in years squared equals the semi-major axis in AU raised to what power?
a) 1 b) 2 c) 3 d) 4 e) 5

10. As a planet approaches perihelion from aphelion, it
a) moves slower (in kilometers per second)
b) moves at a constant speed
c) moves faster (in kilometers per second)
d) at first moves faster, then slows down
e) at first moves slower then speeds up

11. Which observation by Galileo supports the Copernican theory?
a) phases of the Moon
b) retrograde motion
c) the discovery of Pluto
d) the color of Mars
e) the phases of Venus

12. A body in a hyperbolic orbit relative to the Sun
a) will sometimes return to the Sun depending on its speed
b) will always return to the Sun
c) will never return to the Sun
d) is not possible
e) will always fall into the Sun

13. Which planet was discovered by William Herschel in the 18th century?
a) Venus
b) Mercury
c) Neptune
d) Uranus
e) Pluto

14. The orbits of planets cannot actually be perfect ellipses because
a) of their rotations
b) the planets are not spherical
c) of the gravitational pulls of the other planets
d) of the gravitational pulls of the stars
e) the Sun's gravitational field does not behave according to an inverse square law

15. The motion of Uranus led to the discovery of
a) Venus b) Jupiter c) Mars d) Neptune e) the asteroids

16. If you could suddenly shrink the Earth (make the Earth smaller in radius but keep the same mass), the length of the day would
a) increase
b) decrease
c) stay the same
d) increase or decrease depending on the time of year
e) be unpredictable

17. Kepler's third law as generalized by Newton allows you to find
a) the mass of the Sun
b) nothing
c) the chemical composition of Jupiter's atmosphere
d) your latitude
e) the season of the year

18. Pluto was discovered by
a) Albert Einstein
b) Isaac Newton
c) Edmund Halley
d) Clyde Tombaugh
e) William Herschel

19. Kepler's second law of planetary motion is essentially the conservation of
a) angular momentum
b) mass
c) energy
d) mass plus energy
e) electric charge

20. Your weight on a planet depends
a) only on the planet's mass
b) only on the planet's radius
c) on both the planet's mass and radius
d) on neither the planet's mass nor radius
e) on the planet's mass, radius, and magnetic field

Part II. Show all your work.

1. You weigh 100 lbs on Earth. What would you weigh if you could:
a) double the mass of the Earth and keep the radius constant?
b) double the radius of the Earth and keep the mass constant?
c) double both the radius and the mass of the Earth at the same time?

2. You discover a new asteroid, and find that it has an orbital period around the Sun of 8 years. What is the semimajor axis of the orbit? (That is, if the orbit is circular, what is the distance of the asteroid from the Sun?)

3. A satellite orbits Earth at an altitude above the ground of 730 km (450 miles) with a period of 100 minutes. If you increase the distance of the satellite from the center of the Earth by a factor of 10 (to an altitude of 65,000 km (40,000 miles), what is its new period?