Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 21, Problem 29Q
To determine
The speed of a meter stick.
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Students have asked these similar questions
*39 Will the universe continue to expand forever? To attack this
question, assume that the theory of dark energy is in error and that
the recessional speed v of a galaxy a distance r from us is determined
only by the gravitational interaction of the matter that lies inside
a sphere of radius r centered on us. If the total mass inside this
sphere is M, the escape speed v, from the sphere is v. = V2GMIT
(Eq. 13-28). (a) Show that to prevent unlimited expansion, the aver-
age density p inside the sphere must be at least equal to
ЗН
87G
(b) Evaluate this "critical density" numerically; express your an-
swer in terms of hydrogen atoms per cubic meter. Measurements
of the actual density are difficult and are complicated by the pres-
ence of dark matter.
A galaxy is observed to recede from Earth with an approximate speed of 0.81c.
Approximately how far d from Earth is this galaxy? Give an answer in units of megaparsecs (Mpc).
d = ? Mpc
How long ago t was the light that we see emitted by the galaxy? Give an answer in units of years.
t = ? years
Suppose the proper length of a UFO rocketship is 3475 kilometers,
L. Then how fast is the rocketship moving relative to the Earth?
Parameter value: L = 530 km
Give the value of a = (c - v)/c.
OB:
OA:
9.999x10-3
1.170x10-2
OC:
1.369x10-2
OD:
1.602x10-2
but its length observed by a telescope on Earth is
OE:
OF:
1.874x10-2 2.192x10-2
OG:
2.565x10-2
OH:
3.001x10-2
Chapter 21 Solutions
Universe: Stars And Galaxies
Ch. 21 - Prob. 1QCh. 21 - Prob. 2QCh. 21 - Prob. 3QCh. 21 - Prob. 4QCh. 21 - Prob. 5QCh. 21 - Prob. 6QCh. 21 - Prob. 7QCh. 21 - Prob. 8QCh. 21 - Prob. 9QCh. 21 - Prob. 10Q
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