Astronomy 100

Section 2, Fall 2008

Homework D

Answers

1. Venus appears brightest to us when it is in what phase?
e) crescent (Though only partially illuminated, it's close to us when it's in the crescent phase.)

2. For the Solar System, the period of a planet in years squared equals the semi-major axis in AU raised to what power?
c) 3 (Kepler's third law)

3. As a planet approaches perihelion from aphelion, it
c) moves faster (in kilometers per second) (Kepler's second law)

4. Which observation by Galileo supports the Copernican theory?
e) the phases of Venus (which it has only if the Sun is at the center of the Solar System)

5. If you were to triple the mass of the Earth but keep the radius the same you would weigh
b) 3 times as much as you do now (force = [const X M1 X M2]/R**2)

6. Where does the Earth's gravity actually end?
e) nowhere

7. As you descend in an elevator in a tall building, your weight
b) increases (since you are getting closer to the Earth)

8. Orbiting astronauts are weightless because the
e) astronauts and the cabin are both free-falling bodies.

9. If you could cut off the gravity of the Sun and planets (which you cannot), Mars would
b) go flying away from the Solar System in a straight line

10. A body in a hyperbolic orbit relative to the Sun
c) will never return to the Sun

11. Which planet was discovered by William Herschel in the 18th century?
d) Uranus

12. The orbits of planets cannot actually be perfect ellipses because
c) of the gravitational pulls of the other planets

13. The motion of Uranus led to the discovery of
d) Neptune

14. If you could suddenly shrink the Earth (make the Earth smaller in radius but keep the same mass), the length of the day would
b) decrease (The Earth would spin faster because of the conservation of angular momentum.)

15. Kepler's third law as generalized by Newton allows you to find
a) the mass of the Sun

16. Pluto was discovered by
d) Tombaugh

17. Kepler's second law of planetary motion is essentially the conservation of
a) angular momentum

18. Your weight on a planet depends
c) on both the planet's mass and radius (See question 5.)

19. Which particle carries the negative electric charge?
a) only the electron

20. Which particles have nearly the same mass?
b) proton and neutron

21. Which force holds protons and neutrons together in an atomic nucleus?
b) strong

22. Which force holds the electron to the nucleus?
d) electromagnetic

23. The kind of chemical element is determined by the number of
a) protons in the nucleus

24. The second lightest of all elements is
b) helium (with two protons)

25. Which is the correct order from shortest-wave (highest-energy) radiation to longest-wave (lowest-energy) radiation.
b) gamma-ray, X-ray, blue light, red light, radio