When NASA was communicating with astronauts on the Moon, the time from sending on the Earth to receiving on the Moon was 1.28 s. Find the distance from Earth to the Moon. (The speed of radio waves is 3.00 × 10^8 m/s.)
a. 240 000 km
b. 384 000 km
c. 480 000 km
d. 768 000 km
b
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Dark matter is ___
a. a cloud of black holes and brown dwarfs in the galactic halo b. extremely cold, supermassive molecular clouds in the disk c. an unknown type of mass that does not emit or absorb photons d. the substance of which black holes are made e. a theory to explain galactic formation that has been proven wrong
Main-sequence stars have about the same density as the Sun but giant stars have very low densities
a. True b. False Indicate whether the statement is true or false
In a transformer, how many turns are necessary in a 110-V primary if the 24-V secondary has 100 turns?
A) 458 B) 240 C) 110 D) 22 E) 4
Assuming the conditions ripe for life and intelligence abound in the Galaxy, what factor limits the number of galactic civilizations currently in existence?
A) the average survival time of the civilizations B) the lack of metals for technology C) the speed of technological development D) the expansion of the universe E) the number of supernova explosions