Which of the following is an important starting assumption in models of galaxy formation?
A) All galaxies start out as spiral galaxies.
B) Some regions in the universe start out denser than others.
C) Black holes form first, seeding the formation of galaxies.
D) Galaxies form first, then black holes.
B
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In a certain material there is a current of 18 A flowing through a surface to the right, and there is an equal amount of positive and negative charge passing through the surface producing the current. How much negative charge passes through the surface?
a. 9 C/s toward the right b. 9 C/s toward the left c. 18 C/s toward the right d. 18 C/s toward the left e. 36 C/s toward the left
A point charge +Q is located on the x axis at x = a, and a second point charge -Q is located on the x axis at x = -
a. A Gaussian surface with radius r = 2a is centered at the origin. The flux through this Gaussian surface is a. zero because the negative flux over one hemisphere is equal to the positive flux over the other. b. greater than zero. c. zero because at every point on the surface the electric field has no component perpendicular to the surface. d. zero because the electric field is zero at every point on the surface. e. none of the above.
The Eiffel tower in Paris is made primarily of iron, whose coefficient of linear expansion is about 10 × 10^?6/°C. On a cold day when the temperature is –10°C the Eiffel tower is 300 meters tall. Its height on a hot day when the temperature is 40°C is
a. 300.0015 m. b. 300.015 m. c. 300.15 m. d. 301.5 m. e. 315 m.
Which star is the closest if all have the same apparent brightness?
A. a temperature 6000 K main sequence star B. a red giant C. a temperature 10000 K main sequence star D. a main sequence star with a luminosity 100 times that of the Sun E. white dwarf