Which of the following analogies best describes how the structure of the galaxy's spiral arms is maintained?
A) Like military jets flying in formation above a football stadium, the stars in the spiral arms keep a spiral-shaped formation as they orbit the galaxy.
B) Like cars slowing in traffic to look at an accident, stars slow as they pass through the spiral arms.
C) Like a coiling rope, the spiral arms wind up tighter with every galactic rotation.
D) Like the fins of a giant pinwheel toy, the spiral arms carry a set of bright stars around as they sweep through the galaxy.
B
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What is the inductance for an inductor with a reactance of 20
at a frequency of 60 Hz?
A. 12 H B. 19 H C. 3.0 H D. 53 mH E. 27 mH
Determine the effective emissivity of a bank of air 80 cm thick at 20ºC, 80% relative humidity, and 1 atmosphere pressure.
What will be an ideal response?
Slow surface evolution on the moon is limited to
a. low density masses of rock rising from the interior. b. low level meteorite impacts. c. moonquakes disturbing the surface features. d. motion along a network of small faults. e. all of the above
When dark matter was first discovered, some astronomers thought that ?o was greater than one from the extra gravity, favoring what type of universe?
What will be an ideal response?