Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 20, Problem 25E
The 21-cm line can be used not just to find out where hydrogen is located in the sky, but also to determine how fast it is moving toward or away from us. Describe how this might work.
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An object is subjected to a friction force with magnitude 5.49 N, which acts against the object's velocity. What is the work (in J) needed to move the object at constant speed for the following routes?
y (m)
C
B
(5.00, 5.00)
A
x (m)
©
(a) the purple path O to A followed by a return purple path to O
]
(b) the purple path O to C followed by a return blue path to O
]
(c) the blue path O to C followed by a return blue path to O
]
(d) Each of your three answers should be nonzero. What is the significance of this observation?
○ The force of friction is a conservative force.
○ The force of friction is a nonconservative force.
A block of mass m = 2.50 kg is pushed d = 2.30 m along a frictionless horizontal table by a constant applied force of magnitude F = 10.0 N directed at an angle
25.0° below the horizontal as shown in the figure below.
m
(a) Determine the work done by the applied force.
]
(b) Determine the work done by the normal force exerted by the table.
]
(c) Determine the work done by the force of gravity.
]
(d) Determine the work done by the net force on the block.
]
A man pushing a crate of mass m = 92.0 kg at a speed of v = 0.845 m/s encounters a rough horizontal surface of length = 0.65 m as in the figure below. If the coefficient of kinetic friction between the crate and rough surface is 0.357 and he exerts a constant horizontal force of 294 N on
the crate.
e
(a) Find the magnitude and direction of the net force on the crate while it is on the rough surface.
magnitude
direction
---Select---
N
(b) Find the net work done on the crate while it is on the rough surface.
]
(c) Find the speed of the crate when it reaches the end of the rough surface.
m/s
Chapter 20 Solutions
Astronomy
Ch. 20 - Identify several dark nebulae in photographs in...Ch. 20 - Why do nebulae near hot stars look red? Why do...Ch. 20 - Describe the characteristics of the various kinds...Ch. 20 - Prepare a table listing the different ways in...Ch. 20 - Describe how the 21-cm line of hydrogen is formed....Ch. 20 - Describe the properties of the dust grains found...Ch. 20 - Why is it difficult to determine where cosmic rays...Ch. 20 - What causes reddening of starlight? Explain how...Ch. 20 - Why do molecules, including H2 and more complex...Ch. 20 - Why can’t we use visible light telescopes to study...
Ch. 20 - The mass of the interstellar medium is determined...Ch. 20 - Where does interstellar dust come from? How does...Ch. 20 - Figure 20.2 shows a reddish glow around the star...Ch. 20 - If the red glow around Antares is indeed produced...Ch. 20 - Even though neutral hydrogen is the most abundant...Ch. 20 - The terms H II and H2 are both pronounced “H two.”...Ch. 20 - Suppose someone told you that she had discovered H...Ch. 20 - Describe the spectrum of each of the following: A....Ch. 20 - According to the text, a star must be hotter than...Ch. 20 - From the comments in the text about which kinds of...Ch. 20 - One way to calculate the size and shape of the...Ch. 20 - New stars form in regions where the density of gas...Ch. 20 - Thinking about the topics in this chapter, here is...Ch. 20 - Stars form in the Milky Way at a rate of about 1...Ch. 20 - The 21-cm line can be used not just to find out...Ch. 20 - Astronomers recently detected light emitted by a...Ch. 20 - We can detect 21-cm emission from other galaxies...Ch. 20 - We have said repeatedly that blue light undergoes...Ch. 20 - Suppose that, instead of being inside the Local...Ch. 20 - Suppose that, instead of being inside the Local...Ch. 20 - A molecular cloud is about 1000 times denser than...Ch. 20 - Would you expect to be able to detect an H II...Ch. 20 - Suppose that you gathered a ball of interstellar...Ch. 20 - At the average density of the interstellar medium,...Ch. 20 - Consider a grain of sand that contains 1 mg of...Ch. 20 - H II regions can exist only if there is a nearby...Ch. 20 - In the text, we said that the five-times ionized...Ch. 20 - Dust was originally discovered because the stars...Ch. 20 - How would the density inside a cold cloud (T=10K)...Ch. 20 - The text says that the Local Fluff, which...
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