Within cosmology, the critical density is
A. the density that determines whether the Universe expands forever or recollapses.
B. the density of the Universe.
C. the density of the most massive black hole in the Universe.
D. the density of Universes in the multiverse.
E. None of these choices is correct.
Answer: A
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Superconductors most often require
A) low operating temperatures. B) high operating temperatures. C) magnets.
An electrical generating plant operates at a boiler temperature of 225°C and exhausts the unused heat into a nearby river at 25.0°C. If the generating plant has a power output of 850 megawatts (MW) and if the actual efficiency is 3/4 the theoretical efficiency, how much heat per second must be delivered to the boiler? (0°C = 273 K)
a. 8 470 MW b. 4 230 MW c. 2 120 MW d. 2 820 MW e. 1 690 MW
What observational evidence supports the galactic fountain model (which describes how gas cycles between the disk of the galaxy and regions high above the disk)?
A) We have discovered a jet of ionized gas shooting out of the bulge of our galaxy. B) We have discovered that the entire galactic disk is being uniformly "rained on" by cool gas coming from the halo. C) We see hot gas high above the region of the disk near our solar system, along with cool gas that appears to be raining down from the halo. D) We have observed a lot of water molecules in the interstellar medium.
A figure skater rotating at 5.00 rad/s with arms extended has a moment of inertia of 2.25 kg?m2. If the arms are pulled in so the moment of inertia decreases to 1.80 kg?m2, what is the final angular speed?
A) 2.25 rad/s B) 4.60 rad/s C) 6.25 rad/s D) 1.76 rad/s E) 0.81 rad/s