If gravity alone acts to retard the expansion and nothing acts to accelerate it, the Universe is said to be closed if I. gravity is strong enough to stop the expansion in a finite time. II. the density of the Universe is less than the critical density. III. the Universe is finite
a. I & II
b. I & III
c. II & III
d. I, I, & III
e. None of the other choices are correct.
b
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The most common form of gas in the disk of the Milky Way Galaxy is
A) molecular hydrogen. B) gas in hot bubbles. C) atomic hydrogen gas. D) gas in stellar winds.
Why does the Moon not have a magnetic field?
A. The Moon's magnetic field was destroyed by bombardment by planetesimals. B. The Moon lacks an atmosphere. C. It rotates very slowly and has a cold interior. D. Any field the Moon could generate is overwhelmed by Earth's field. E. Only planets can have magnetic fields.
Which moon of Neptune has a thin atmosphere and frosty polar caps?
a. Triton b. Titan c. Io d. Charon
A battery is rated at 12 V and 160 A-h. How much energy does this battery store?
A) 1.9 kJ B) 6.0 kJ C) 1.9 MJ D) 6.9 MJ