Mercury is geologically inactive because it:
A) has lost much of its internal heat.
B) has a very dense atmosphere.
C) is too big to be geologically active.
D) is the closest planet to the Sun.
A
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An object of mass m traveling at speed 
in the +x direction hits an identical object at rest. Characterize each of the collision outcomes shown below as being (A) absurd or (C) credible. (The collisions are not necessarily elastic, but they are not super-elastic.)
What causes stars to twinkle?
A) Stars constantly vary in brightness as they expand and contract. B) Interstellar gas along the line of sight to the star absorbs different amounts of radiation. C) The human eye has difficulty seeing faint objects. D) Moving gases in Earth's atmosphere randomly bend light rays from stars.
What is the apparent path of the Sun along the celestial sphere?
a)the ecliptic b)a eclipse c) retrograde motion
A proton (being 1836 times heavier than an electron) gains how much energy when moving through a potential increase of one volt?
A) 1836. eV B) 1. eV C) 0 eV D) 1. Joule E) 1836. J