What fraction of the mass needed to halt expansion is known to exist in the form of visible mass in the universe?
A) 1 percent
B) 4 percent
C) 22 percent
D) 74 percent
E) 100 percent
A
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Science offers final explanations of the universe and its phenomena
Indicate whether the statement is true or false
Observations of the tiny irregularities in the cosmic microwave background support the idea that the Universe
A. will continue to expand forever. B. will collapse in the distant future. C. is composed primarily of matter, rather than antimatter. D. contains no dark matter. E. is composed primarily of neutrinos.
The fusion reaction 
releases 17.6 MeV of energy. The mass of 2H is 2.01410 u, the mass of 4He is 4.00260 u, and the mass of 1n is 1.00866 u. What is the mass of 3H?
A. 2.99716 u B. 3.01605 u C. 3.03494 u D. 3.04221 u E. 2.99982 u
How fast must a hydrogen atom be traveling for its kinetic energy to be just enough to excite the ground-state atom to its first excited state in a collision? (1 eV = 1.60 × 10-19 J, mH ? mproton = 1.67 × 10-27 kg)
A) 44.2 km/s B) 21.7 km/s C) 66.5 km/s D) 113 km/s E) 51.0 km/s