The crossover point from radiation to matter domination occurred
A) when the strong force separated from the other two forces.
B) with the emission of the cosmic background radiation.
C) about 50,000 years after the Big Bang, at a temperature of about 16,000 K.
D) with the creation of neutrons and protons, at about 1013 K.
E) with the creation of electrons and positrons at about 6 × 109 K.
C
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What are interstellar grains?
A. the material out of which exoplanets are formed B. droplets of material that have condensed out of the Solar nebula C. tiny dust particles that are part of interstellar clouds D. leftover fragments of planetesimals that are blown out of the Solar System
The time between the vernal equinox and the autumnal equinox is somewhat greater than the time between the autumnal equinox and the vernal equinox. This is a result of Kepler's ________ law.
A. First B. Second C. Third D. Fourth
Work
a)can be measured in watts. b)has the units of force x time. c)is a vector quantity. d)has the units of N-m.
A vector lies in the x-y plane. For what orientations will both components be negative?
1.The vector lies between 180° and 270° from the x-axis. 2.The vector lies between 0° and 90° from the x-axis. 3.The vector lies between 90° and 180° from the x-axis. 4.None. Just like for vector magnitudes, components are always positive.