The critical density of the universe is the
A) total density of matter and energy needed to give the universe a "flat" geometry (in spacetime).
B) measured average density of matter in the universe.
C) density of matter necessary for stars and galaxies to form.
D) density value at which the total density of matter precisely equals the total density of antimatter.
A) total density of matter and energy needed to give the universe a "flat" geometry (in spacetime).
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The _____________ line in a phase diagram separates the ?-phase field from the ?+?-phase field, and it gives the maximum solubility of the B-type atoms in the A-type crystal.
Fill in the blank(s) with the appropriate word(s).
A submarine must travel how fast (with respect to the water) and be pointed in what direction such that it moves 10. m/s directly Northward (relative to the Earth) if the water moves westward at 5.0 m/s?
What will be an ideal response?
The mass of an apple on the Earth is 0.2 kg. On the Moon, the mass of the same apple would be
A. greater than zero but less than 0.2 kg. B. greater than 0.2 kg. C. 0.2 kg. D. zero.
Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass?
A) All the material will have completely decayed. B) You'll have 0.75 kilogram of the radioactive substance remaining. C) You'll have 0.25 kilogram of the radioactive substance remaining. D) You'll have 0.5 kilogram of the radioactive substance remaining.