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Physics 002 Final Examination 14 December, 2002.
Time allowed: 90 minutes Total: 70 marks

Name:

Student ID:
A



Data table:
1 parsec
3.26 light years

1 parsec
206,265 AU

1 Astronomical Unit
1.50 1011 m

Speed of light
3 108 m/s

Universal gravitational constant
6.67 10-11 N.m2/kg2

Mass of Sun MO
1.99 1030 kg

Our distance from the center of Milky Way
8,500 pc




Part A Multiple choice (18 marks):

(1) According to the theory of general relativity, gravity is caused by
A. the equivalence principle.
B. the change in mass of a moving body.
C. the curvature of space-time.
D. the constant speed of light.
E. none of the above
Ans.__C__

(2) Massive stars cannot generate energy through iron fusion because
A. iron fusion requires very high density.
B. stars contain very little iron.
C. no star can get hot enough for iron fusion.
D. iron is the most tightly bound of all nuclei.
E. massive stars supernova before they create an iron core.
Ans.__D__

(3) Pulsars cannot be spinning white dwarfs because
A. white dwarfs are not that common.
B. white dwarfs are not dense enough.
C. white dwarfs do not have magnetic fields.
D. a white dwarf spinning that fast would fly apart.
E. all of the above
Ans.___D__

(4) An isolated black hole in space would be difficult to detect because
A. there would be no light source nearby.
B. it would not be rotating rapidly.
C. it would be stationary.
D. very little matter would be falling into it.
E. there would be very few stars behind whose light it could block out.
Ans.__D___




(5) The mass of a single galaxy might be found by
A. the double galaxy method.
B. the rotation curve method.
C. the cluster method.
D. any of these methods.
E. none of these methods.
Ans.__B__

(6) The universe is said to be closed if

I.
gravity is strong enough to stop the expansion in a finite time.

II.
the density of the universe is less than the critical density.

III.
the universe is finite.




A. I & II
B. I & III
C. II & III
D. I, I, & III
E. none of the above
Ans.__B__
Part B True and False.(16 marks):
(6-14) Read carefully the following italicized paragraphs abridged from Scientific American. The theme is about stellar collisions.

For much of the 20th century, the notion that stellar collisions seemed ludicrous to astronomers. In fact, it has been calculated that not a single one of the 100 billion stars in the disk of our galaxy has ever run into another star. This conclusion applies to the environs of the sun but not to other, more exotic parts of the Milky Way, such as dense star clusters.
The Uhuru satellite, launched in 1970 to survey the sky for x-ray emitting objects, discovered about 100 bright sources in the Milky Way. Fully 10 percent were in the densest type of star cluster, globular cluste