Before the decoupling
A) the Universe was transparent to radiation.
B) the Universe was opaque to radiation.
C) protons and electrons combined to form atoms.
D) there was more helium than hydrogen.
E) deuterium produced electrons and positrons.
B
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A photon of frequency
Hz has what energy?
A. 1.26 eV B. 1.93 eV C. 2.11 eV D. 2.65 eV E. 3.17 eV
Two examples of a longitudinal wave are __________ and __________
Fill in the blank(s) with correct word
A typical galaxy is a
A) collection of millions or billions of stars, bound together by gravity and orbiting a common center. B) large, glowing ball of gas powered by nuclear energy. C) nearby object orbiting a planet. D) relatively small, icy object orbiting a star. E) system consisting of one or a few stars orbited by planets, moons, and smaller objects.
Mary and Debra stand on a snow-covered roof. They both throw snowballs with the same initial speed, but in different directions. Mary throws her snowball downward, at 30° below the horizontal; Debra throws her snowball upward, at 30°
When the snowballs reach the ground below, A) Debra's snowball will have a higher speed than Mary's. B) Mary's snowball will have a higher speed than Debra's. C) Both snowballs will hit the ground with the same speed. D) Debra's snowball never hits the ground since it is thrown upwards. E) Mary's snowball never hits the ground since it is thrown downwards.