How do stars on the main sequence obtain their energy?
A) from chemical reactions
B) from gravitational contraction
C) by converting hydrogen to helium in their cores
D) by converting helium to carbon, nitrogen, and oxygen
E) from nuclear fission
C) by converting hydrogen to helium in their cores
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Determine the heat capacity (in calories/°C) of a lake containing one million gallons (approximately 4 million kilograms) of water at 15°C.
A. 4 × 106 B. 4 × 109 C. 4 × 103 D. 1 × 103 E. 4 × 102
A sample containing 4.0 × 1018 atoms of a radioactive isotope decays with a half-life of 2.3 years. How many undecayed atoms are left after 3.7 years?
A) 2.5 × 1018 B) 1.7 × 1018 C) 1.3 × 1018 D) 1.1 × 1018
A string on a guitar is plucked. If, at this instant, someone touches this guitar string at its center, at which of its harmonics given below would the string be able to vibrate? sity?
1.at the first harmonic only 2.at the first and third harmonics 3.at the second and fourth harmonics 4.at the first and second harmonics
The great contribution of Tycho Brahe was to
A) observe planetary positions with sufficient accuracy that later enabled Kepler to discover the laws of planetary motion. B) discover four moons orbiting Jupiter, thereby lending strong support to the idea that the Earth is not the center of the universe. C) offer the first detailed model of a Sun-centered solar system, thereby beginning the process of overturning the Earth-centered model of the Greeks. D) discover that planets orbit the Sun in elliptical orbits with varying speed.