If the density of the Universe is less than the critical density, then
A. the Universal expansion will eventually stop sometime in the future.
B. the Universe will eventually stop expanding, and then begin to collapse until it ends in a Big Crunch.
C. the Universe will not change because its evolution does not depend on the critical density.
D. the Universe will expand forever.
Answer: D
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When light goes from a material with a lower index of refraction n1 into a material with a higher index of refraction n2 with an angle of incidence of 
which of the following is true?
A. the angle of refraction is more than
B. the angle of refraction is less than
C. total internal reflection may occur
D. the angle of refraction is more than
and total internal reflection may occur
E. the angle of refraction is less than
and total internal reflection may occur
Rising air expands and cools. If the air mass cools below its dew point temperature, the air mass
A) reaches 100% relative humidity, and water vapor evaporates. B) reaches 100% relative humidity, and water vapor may condense to form clouds. C) stops moving upward and relative humidity climbs to 100%. D) continues to cool at the environmental lapse rate.
Energy Levels: What is the ionization energy of singly-ionized helium, which has 2 protons?
A. 54.4 eV B. 13.6 eV C. 27.2 eV D. 6.80 eV E. 36.4 eV
A small sphere attached to a light rigid rod rotates about an axis perpendicular to and fixed to the other end of the rod. Relative to the positive direction of the axis of rotation, the angular positions of the sphere are negative, its angular velocity is negative, and its angular acceleration is negative. The sphere is
a. rotating clockwise and slowing down. b. rotating counterclockwise and slowing down. c. rotating clockwise and speeding up. d. rotating counterclockwise and speeding up. e. first rotating counterclockwise and then clockwise.