Earth's first atmosphere was rich in water vapor but poor in free oxygen. The atmosphere became more oxygenated with the
A) development of the ozone layer.
B) emergence of stromatolites that developed a simple version of photosynthesis.
C) emergence of gases from volcanic eruptions.
D) both A and B.
Answer: B
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Approximately what percentage of mass-energy of infalling matter can be converted to thermal energy when the matter is falling into a supermassive black hole?
A) about the same as that converted by hydrogen fusion B) much less than that converted by hydrogen fusion C) much more that converted by hydrogen fusion
An assault rifle fires an eight-shot burst in 0.40 s. Each bullet has a mass of 7.5 g and a speed of 300 m/s as it leaves the gun. What is the average recoil force on the gun during that burst?
A) 45 N B) 5.6 N C) 16 N D) 2.0 N E) 23 N
A violation of the second law of thermodynamics would occur if
a. a ball lying on the ground started to bounce. b. transfer of energy by heat moved energy from an object at low temperature to an object at a higher temperature. c. a refrigerator heated the air in the room in which the refrigerator is located. d. any of the above occurred. e. (a) or (b) occurred, but not (c).
A magnifying lens with a focal length of 10 cm has what maximum magnification? (Assume the near point is 25 cm). Do not use the approximation formula
a. 3.5 c. 7.1 b. 2.5 d. 3.0