Physics For Scientists And Engineers With Modern Physics, 9th Edition, The Ohio State University
9th Edition
ISBN: 9781305372337
Author: Raymond A. Serway | John W. Jewett
Publisher: Cengage Learning
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Chapter 46, Problem 49P
To determine
By what factor the Universe will expand in future.
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1. The current (critical) density of our universe is pe = 10-26kg/m³. Assume the universe is
filled with cubes with equal size that each contain one person of m = 100kg. What would
the length of the side of such a cube have to be in order to give the correct critical density?
How many hydrogen atoms would you need in a box of 1 m³ to reach the critical density?
The matter we know, which consists mostly of hydrogen, constitutes only 4.8% of the current
critical energy density of our universe. So how many hydrogen atoms are actually in a box
of 1 m3 in our universe? Deep space is very empty and a much better vacuum than we can
obtain on earth in a laboratory.
An astronomer observed the motions of some galaxies. Based on his observations, he made the following statements. Which one of them is most likely to be false? Take Hubble's constant to be 67 km/s/Mpc.
A. A galaxy observed to be moving away from us at a speed of 70 km/s is at a distance of about 1 Mpc from us.
B. A galaxy observed to be moving away from us at a speed of 700 km/s is at a distance of about 10 Mpc from us.
C. A galaxy observed to be moving away from us at a speed of 7000 km/s is at a distance of about 100 Mpc from us.
D. A galaxy observed to be moving away from us at a speed of 70000 km/s is at a distance of about 1 Gpc from us.
Is the answer D? Thank you!
A galaxy's rotation curve is a measure of the orbital speed of stars as a function of distance
from the galaxy's centre. The fact that rotation curves are primarily flat at large galactocen-
tric distances (vrot(r) ~ constant) is the most common example of why astronomer's believe
dark matter exists. Let's work out why!
Assuming that each star in a given galaxy has a circular orbit, we know that the accelera-
tion due to gravity felt by each star is due to the mass enclosed within its orbital radius r and
equal to v?/r. Here, ve is the circular orbit velocity of the star. (a) Show that the expected
relationship between ve and r due to the stellar halo (p(r) xr-3.5) does not produce a flat
rotation curve. (b) Show that a p(r) ∞ r¯² density profile successfully produces a flat ro-
tation curve and must therefore be the general profile that dark matter follows in our galaxy.
Chapter 46 Solutions
Physics For Scientists And Engineers With Modern Physics, 9th Edition, The Ohio State University
Ch. 46.2 - Prob. 46.1QQCh. 46.5 - Prob. 46.3QQCh. 46.5 - Prob. 46.4QQCh. 46.8 - Prob. 46.5QQCh. 46.8 - Prob. 46.6QQCh. 46 - Prob. 1OQCh. 46 - Prob. 2OQCh. 46 - Prob. 3OQCh. 46 - Prob. 4OQCh. 46 - Prob. 5OQ
Ch. 46 - Prob. 6OQCh. 46 - Prob. 7OQCh. 46 - Prob. 8OQCh. 46 - Prob. 1CQCh. 46 - Prob. 2CQCh. 46 - Prob. 3CQCh. 46 - Prob. 4CQCh. 46 - Prob. 5CQCh. 46 - Prob. 6CQCh. 46 - Prob. 7CQCh. 46 - Prob. 8CQCh. 46 - Prob. 9CQCh. 46 - Prob. 10CQCh. 46 - Prob. 11CQCh. 46 - Prob. 12CQCh. 46 - Prob. 13CQCh. 46 - Prob. 1PCh. 46 - Prob. 2PCh. 46 - Prob. 3PCh. 46 - Prob. 4PCh. 46 - Prob. 5PCh. 46 - Prob. 6PCh. 46 - Prob. 7PCh. 46 - Prob. 8PCh. 46 - Prob. 9PCh. 46 - Prob. 10PCh. 46 - Prob. 11PCh. 46 - Prob. 12PCh. 46 - Prob. 13PCh. 46 - Prob. 14PCh. 46 - Prob. 15PCh. 46 - Prob. 16PCh. 46 - Prob. 17PCh. 46 - Prob. 18PCh. 46 - Prob. 19PCh. 46 - Prob. 20PCh. 46 - Prob. 21PCh. 46 - Prob. 22PCh. 46 - Prob. 23PCh. 46 - Prob. 24PCh. 46 - Prob. 25PCh. 46 - Prob. 26PCh. 46 - Prob. 27PCh. 46 - Prob. 28PCh. 46 - Prob. 29PCh. 46 - Prob. 30PCh. 46 - Prob. 31PCh. 46 - Prob. 32PCh. 46 - Prob. 33PCh. 46 - Prob. 34PCh. 46 - Prob. 35PCh. 46 - Prob. 36PCh. 46 - Prob. 37PCh. 46 - Prob. 38PCh. 46 - Prob. 39PCh. 46 - Prob. 40PCh. 46 - Prob. 41PCh. 46 - Prob. 42PCh. 46 - Prob. 43PCh. 46 - Prob. 44PCh. 46 - The various spectral lines observed in the light...Ch. 46 - Prob. 47PCh. 46 - Prob. 48PCh. 46 - Prob. 49PCh. 46 - Prob. 50PCh. 46 - Prob. 51APCh. 46 - Prob. 52APCh. 46 - Prob. 53APCh. 46 - Prob. 54APCh. 46 - Prob. 55APCh. 46 - Prob. 56APCh. 46 - Prob. 57APCh. 46 - Prob. 58APCh. 46 - An unstable particle, initially at rest, decays...Ch. 46 - Prob. 60APCh. 46 - Prob. 61APCh. 46 - Prob. 62APCh. 46 - Prob. 63APCh. 46 - Prob. 64APCh. 46 - Prob. 65APCh. 46 - Prob. 66APCh. 46 - Prob. 67CPCh. 46 - Prob. 68CPCh. 46 - Prob. 69CPCh. 46 - Prob. 70CPCh. 46 - Prob. 71CPCh. 46 - Prob. 72CPCh. 46 - Prob. 73CP
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- 4arrow_forwardPretend that galaxies are spaced evenly, 7.0 Mpc apart, and the average mass of a galaxy is 1.0 ✕ 1011 M. What is the average density (in kg/m3) of matter in the universe? (Note: The volume of a sphere is 4/3pieR^3 and the mass of the sun is 2.0 ✕ 1030 kg.) ______ kg/m^3 Which model universe does this density value support? A: open B: flat C: closedarrow_forwardPretend that galaxies are spaced evenly, 8.0 Mpc apart, and the average mass of a galaxy is 1.0 ✕ 1011 M. What is the average density (in kg/m3) of matter in the universe? Which model universe does this density value support?arrow_forward
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