Concerning dark energy, we do know
A) combined with dark matter, it will ultimately produce a closed universe.
B) its density remains constant over time, so it is not important in the early universe.
C) that it is created when matter annihilates anti-matter.
D) that it was revealed with Type II supernovae distances in the late 1990s.
E) that it makes up 90% of all the matter and energy in the whole universe.
B
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Thin Films: Light reflects off the surface of Lake Superior. What phase shift does it undergo?
A. 0° B. 90° C. 180° D. 270° E. It does not undergo any phase shift.
Resistance and Resistivity: If a quantity you calculated has units of 
what is that quantity?
A. potential B. resistivity C. resistance D. capacitance E. current
A box is sliding down an incline tilted at a 12.0° angle above horizontal. The box is initially sliding down the incline at a speed of 1.50 m/s. The coefficient of kinetic friction between the box and the incline is 0.340
How far does the box slide down the incline before coming to rest? A) 0.920 m B) 2.33 m C) 1.78 m D) 0.720 m E) The box does not stop. It accelerates down the plane.
As an interstellar cloud of hydrogen gas shrinks in size, its rate of rotation
A) increases, because its total energy is conserved. B) decreases, because the force of gravity strengthens as the cloud shrinks. C) increases, because its angular momentum is conserved. D) decreases, because its angular momentum is conserved. E) increases, because the force of gravity strengthens as the cloud shrinks.