What observation has prompted astronomers to ponder the possible existence of dark energy?
a. Discovery of quasars
b. Discovery of superclusters
c. Supernovae appear fainter than expected at large redshifts.
d. Uniform nature of the cosmic microwave background (CMB).
C
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The light from a distant star is shifted such that the peak of its spectrum, at 620 nm, is shifted to 635 nm. What is its radial velocity relative to Earth?
A. -0.11c B. -0.024c C. -0.15c D. -0.012c
Two pipe columns are required to have the same Euler buckling load Pcr. Column 1 has flexural rigidity EI and height L1; column 2 has flexural rigidity (4/3) EI and height L2. The ratio (L2/L1) at which both columns will buckle under the same load is approximately:
(A) 0.55
(B) 0.72
(C) 0.81
(D) 1.10
An 80-kg man is skating northward and happens to suddenly collide with a 20-kg boy who is ice skating toward the east. Immediately after the collision, the man and boy are seen to be moving together at 2.5 m/s in a direction 60° north of east
How fast was the boy moving just before the collision?
Granulation is caused by:
A) shock waves in the corona. B) rising and falling currents of gas in and just below the photosphere. C) the solar wind flowing away from the corona. D) the temperature variability in the chromosphere, which causes sudden heating.