ASTRO 001.1  FALL 2001   EXAM  2               FORM A

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Multiple Choice.  In each case, please choose the one best answer.

1. When a rocket in space fires its engine so that hot exhaust is expelled straight out the back, the force necessary to accelerate the exhaust gases __________.

a) would be called a gravitational force
b) is zero
c) is less than the force accelerating the rocket, but greater than zero
d) is greater than the force accelerating the rocket
e) is equal to the force accelerating the rocket

2. If we measure the wavelengths of emission and absorption lines from the same gas (e.g., hydrogen), we find that (ignoring any Doppler shifts) __________.

a) the patterns of lines are identical
b) the patterns of lines are completely different
c) the emission lines are all shifted to longer wavelengths
d) the emission lines are all shifted to shorter wavelengths

3. The best shape for the cross-section of a large astronomical mirror in order to produce the sharpest images of distant objects is __________.

a) a perfectly flat, smooth surface
b) a spherical shape
c) an elliptical shape
d) a parabolic shape

4. A low density gas confined to a narrow glass tube is heated by an electric current so that it glows;  this situation describes a ‘neon’ light.  What kind of spectrum would you expect to observe were you to pass the light of this source through a prism?

a) Continuous
b) Absorption line
c) Emission line
d) Black body

5. In what way do electromagnetic (em) waves differ from other kinds of waves (e.g., sound waves)?

a) em waves have only one wavelength
b) em waves have only one frequency
c) em waves  have zero amplitude
d) em waves can travel in a vacuum

6. The sun radiates approximately like a blackbody.  Suppose the sun’s temperature were half its present value (i.e., 2900 K instead of 5800 K).  How would the total amount of energy radiated per second by the sun change?

a) It would be equal to its present value.
b) It would be less than half its present value.
c) It would be exactly half its present value.
d) It would be twice its present value.
e) It would be more than twice its present value.

6. What does temperature measure?

a) the average mass of atoms in a substance
b) the average size of atoms in a substance
c) the average kinetic energy of atoms in a substance
d) the total kinetic energy of atoms in a substance
e) the total number of atoms in a substance

8. Considering Einstein’s famous equation, E = mc2, which of the following statements is true?

a) Mass can be converted into energy, but energy cannot be converted into mass.
b) It takes a large amount of mass to produce a small amount of energy.
c) A small amount of mass can be turned into a large amount of energy.
d) You can convert mass into energy if you can accelerate the mass to the speed of light.
e) One kilogram of mass yields 1 joule of energy.

9. Which of the following statements about electrons in an atom is not true?

a) Electrons orbit the nucleus much like planets orbit the Sun.
b) Within the atom, an electron can have only particular energies.
c) Electrons can jump between energy levels in an atom only if they receive or give up an amount of energy equal to the difference in energy between two energy levels.
d) An electron carries a negative electrical charge.

10. Kepler’s 2nd law, which states that as a planet moves around its orbit it sweeps out equal area in equal times means that __________.

a) a planet travels fast when it is close to the Sun and slow when it is far from the Sun
b) a planet travels fast when it is far from the Sun and slow when it is close to the Sun
c) planets have circular orbits
d) the orbit period of a planet depends on the planet’s average distance from the Sun
e) the orbit speed of a planet does not vary around the orbit, even for highly eccentric orbits

11. The basic difference between radio waves, visible light and x-rays is the wavelength.

a) True
b) False

12. A light source is known to emit at a single wavelength in the green part of the visible spectrum.  The source is moving away from you and you notice that is doesn’t look green.  Which of the following is the most likely observed color?

a) Yellow.
b) Blue.

13. Suppose the angular separation of two stars in the sky is smaller than the angular resolution of your eyes.  How will the stars appear to your eyes?

a) You will not be able to see these two stars at all.
b) The two stars will look like a single point of light.
c) You will see two distinct points of light.
d) You will see only the brighter of the two stars, and not the dimmer.

14. Which of the following statements correctly describes the law of conservation of energy?

a) An object always has the same amount of energy.
b) Energy can change between many different forms, such as potential, kinetic and thermal, but it is ultimately destroyed.
c) The total quantity of energy in the universe never changes.
d) It is not really possible for an object to gain or lose potential energy, because energy cannot be destroyed.

15. How can an electron in an atom lose energy to go from a higher energy level to a lower energy level?

a) It loses kinetic energy.
b) It releases a photon equal in energy to the energy lost by the electron.
c) It absorbs a photon equal in energy to the energy lost by the electron.
d) It loses gravitational potential energy.
e) It exchanges electrical potential energy for kinetic energy.

16. Which of the following is not a close approximation to a continuous emitter?

a) A hot, thin gas.
b) A star.
c) A filament in an ordinary (incandescent) light bulb.
d) You.
e) A planet.

17. Studying a spectrum of a star’s light can tell us a lot about the star.  All of the following statements are true except one.  Which one is not true?

a) The peak of the star’s continuous emission tells us its temperature.
b) The total amount of light in the spectrum tells us the star’s radius.
c) We can identify chemical elements present in the star by recognizing in the star’s spectral lines.
d) We can look at the shift of the lines of the star’s spectrum to determine whether the star is moving toward us or away from us.

18. A substance said to be in the plasma state would be characterized by which of the following conditions?

a) Nearly all atoms would be neutral.
b) Nearly all atoms would be ionized.
c) The substance must be at very low temperature.
d) The atoms would be very close together.
e) The substance would have to be of very high density.

19. An orange looks orange in color because __________.

a) of its temperature
b) it selectively absorbs orange wavelengths while reflecting other wavelengths
c) it selectively reflects orange wavelengths while absorbing other wavelengths
d) the atoms in its skin are ionized
e) it selectively transmits all colors except orange

Imagine a 4-lb brick and a 0.1 lb ‘nerf’ (foam-rubber) ball dropped simultaneously from a position 100 ft above Earth’s surface.  In the absence of air resistance, we find that brick and ball fall toward the ground with a common acceleration (the ‘acceleration due to gravity’).  Please refer to this diagram in responding to Question 20.
 
 

            Ball          Brick


 
 

20. The above result can be understood by assuming that __________.

a) the force exerted on brick and ball are equal
b) the force exerted on the brick exceeds the force exerted on the ball
c) the force exerted on the ball exceeds the force exerted on the brick
d) both  brick and ball are subject to zero force

21. Which of the properties of a pencil would certainly change if you took it to the Moon?

a) Its weight.
b) Its mass.
c) Its mass and its weight.
d) Its length.
e) Its color.
 


 
 
 

Here’s the energy level diagram for the hydrogen atom.  Several possible transitions of electrons between energy levels are indicated by numbered arrows (1 – 5).  Please refer to this diagram when responding to Questions 22 - 25.

22. Which transition represents an electron that absorbs a photon with 10.2 eV of energy?

a) 1
b) 2
c) 3
d) 4
e) 5

23. If transition #5 involves a (visible light) green photon, then which of the following is closest to the color of the photon associated with transition #4?

a) red
b) blue
c) violet

24. Which transition, as shown, is not possible?

a) 1
b) 2
c) 3
d) 4
e) 5

25. Given that transition #5 is associated with a (visible light) green photon, in what part of the em spectrum would we find the photon associated with transition #1?

a) Very short wavelength visible light.
b) Very long wavelength visible light.
c) The infrared part of the em spectrum.
d) The ultraviolet part of the em spectrum.
e) The radio wavelength part of the em spectrum.

26. The human eye can detect __________ of the electromagnetic spectrum.

a) all
b) only the shortest wavelengths
c) only the longest wavelengths
d) only a very small part of

27. The astronomer who made the very accurate naked-eye observations of Mars (and other planets) that led to our present picture of planetary orbits was __________.

a) Galileo
b) Kepler
c) Newton
d) Copernicus
e) Brahe

28. Galileo’s discovery of the moons of Jupiter was significant support for the heliocentric hypothesis of the solar system because it showed that __________.

a) gravity could hold a moon in its orbit
b) Jupiter does not move
c) a planet can have more than one moon
d) Jupiter must be much more massive than Earth
e) objects could orbit bodies other than Earth

29. Whereas the Greeks and their predecessors claimed that all planets orbit a stationary Earth on circles, Copernicus argued that all planets (including Earth) follow elliptical orbits about a stationary sun.

a) True
b) False

30. Astronomers spend most of their time looking through telescopes.

a) True
b) False
 
 
 


 
 

A ‘snapshot’ of waves produced on a pond by a source (S) is depicted above.  Please refer to this diagram when responding to Questions 31 – 32.

31. The source in moving in what direction?

a) To the left (<--)
b) To the right (-->)
c) Up
d) Down

32. An observer at X in the diagram would find the wave’s __________ to be __________ than if the source were not moving.

a) speed; larger
b) speed; smaller
c) frequency; smaller
d) frequency; larger
e) wavelength; smaller

33. If a small satellite goes around Earth in a perfectly circular orbit, then according to Newton’s laws of motion, it __________.

a) is constantly being accelerated
b) is not subject to any force
c) must keep a rocket firing to keep up its speed
d) must have a constant velocity
 
 


 
 

Consider three orbits about the sun, depicted above (labeled A, B and C).  Note that all have the same major axis (i.e., long-dimension) length of 6 AU.  Please refer to this diagram when responding to Questions 34 - 36.

34. For which orbit is the orbit period longest?

a) A
b) B
c) C
d) Orbit periods are identical.

35. Which orbit has the largest eccentricity?

a) A
b) B
c) C
d) Eccentricities are identical.

36. Which orbit best depicts the shape (if not the size) of Earth’s orbit?

a) A
b) B
c) C
 
 
 
 
 


 
 

37. Here’s a picture of Earth.  An object (baseball, bowling ball, etc. ) is launched from point X in the direction indicated by the solid arrow.  Five numbered lines/curves describe possible trajectories of the object; note that #2 is a straight line.  Which of these can be ruled out?  [Assume X lies so far from Earth that air resistance is effectively zero.]

a) 1 only
b) 2 only
c) 1 and 2
d) 1, 2 and 5
e) 5 only

38. If an object is accelerated, what must change?

a) Its speed must increase.
b) It speed, which could either increase or decrease.
c) Its direction of motion.
d) Either its speed, or direction of motion, or both.

39. On a planet with twice Earth’s radius, you would weigh __________.

a) exactly what you weigh on Earth’s surface
b) more than what you weigh on Earth’s surface
c) less than what you weigh on Earth’s surface
d) a value which we cannot determine unless we know the other planet’s mass, too.
 
 

Spectra labeled 1, 2 and 3 are depicted above.  Spectrum 2 originates in a light source attached to Earth; spectra 1 and 3 originate in the light of two stars.  Please refer to this diagram when responding to Question 40 - 41.

40. Which star is moving away from Earth?

a) 1
b) 3
c) Neither star is moving away from Earth.
d) Both stars are moving away from Earth.

41. Suppose these spectra are emission line spectra.  What is most likely to be the color of the lines at the far right-hand end of the spectra (lines labeled ‘X’)?

a) violet
b) green
c) black
d) white
e) red

42. A force applied to a brick results in an acceleration of 4.0 m/s/s.  The same force applied to two bricks glued together results in what acceleration?  [Assume the glue adds negligible mass.]

a) 0 m/s/s
b) 4 m/s/s
c) 2 m/s/s
d) 8 m/s/s
e) 0.25 m/s/s
 
 
 


 

 Here’s the (rather complicated) spectrum of the planet Mars, found in your textbook. Some of the more prominent features are labeled with numbers (1, 2, 3, 4).  Please refer to this diagram when responding to Questions 43 – 44.

43. Which spectrum feature represents emission from the warm surface of Mars?

a) 1
b) 2
c) 3
d) 4

44. Which spectrum feature results from absorption of photons by Mars’ atmosphere?

a) 1
b) 2
c) 3
d) 4
 
 
 
 
 
 


 
 
 
 

A star (A) and a planet (B) orbit a common point (+), as depicted above.  Numbers 1, 2, 3 and 4 refer to points on the orbits.   Please refer to this diagram when responding to Questions 45 - 48.

45. According to this diagram, which of the two – star or planet – is the more massive?

a) The star is the more massive.
b) The planet is the more massive.
c) Their masses are equal.

46. The star exerts a gravitational force on the planet; the planet likewise exerts a gravitational force on the star.  How do these forces compare?

a) The forces are equal.
b) The star exerts a greater force on the planet than the planet exerts on the star.
c) The planet exerts a greater force on the star than the star exerts on the planet.
d) We lack the information required to answer this question.

47. The planet (B) moves to point 1.  What’s the most likely position of A?

a) 2
b) 3
c) 4
d) A doesn’t move at all – it remains in the position depicted above.

48. Suppose the mass of A increases, while the orbits remain unchanged in size. How must the orbit period of this system change?

a) The orbit period remains unchanged.
b) The orbit period decreases.
c) The orbit period increases.

49. A planet orbiting the Sun at twice Earth’s average distance from the Sun would have orbit period ___________.

a) 1 year
b) exactly 2 years
c) more than 2 years
d) less than 1 year

50. The most important telescope function is the ability to __________.

a) Magnify.
b) See fine detail.
c) Make objects appear brighter.