Most active galactic nuclei are powered by
A) supermassive black holes.
B) a large number of supernovae.
C) mergers of compact objects.
D) black hole mergers.
E) extra-terrestrial civilizations.
A
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A refrigerator extracts 65 J of heat from a heat reservoir at
If the coefficient of performance of the refrigerator is 2.5, then how much work is needed to run the refrigerator?
A. 26 J B. 48 J C. 75 J D. 90 J
Each box in this figure represents a different level of structure in our universe. Each box is labeled with one of the numbers 1—5. Which box represents the Milky Way Galaxy?
A) 1 B) 2 C) 3 D) 4 E) 5
As an electromagnetic wave travels through free space, its speed can be increased by:
a. increasing its frequency. b. increasing its energy only. c. increasing both its energy and momentum. d. None of the above will increase its speed.
When a ball rises vertically to a height h and returns to its original point of projection, the work done by the gravitational force is
a. 0. b. -mgh. c. +mgh. d. -2mgh. e. +2mgh.