Why didn't oxygen begin to accumulate in the atmosphere until approximately 1.5 billion years after life appeared on Earth?
A) Early forms of animal life consumed the oxygen.
B) Early forms of plant life consumed oxygen.
C) All the oxygen produced by life went into making the ozone layer.
D) Oxygen produced by life was removed from the atmosphere by oxidation reactions with surface rocks.
E) Oxygen produced by life was removed from the atmosphere by dissolving in the ocean.
D
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A ball, of mass 100. g, is dropped from a height of 12. m. Its momentum when it strikes the ground is
A) 1.5 kg?m/s. B) 4.8 kg?m/s. C) 3.3 kg?m/s. D) 2.4 kg?m/s. E) 1.8 kg?m/s.
How far from a lens of focal length 50.0 mm must the object be placed if it is to form a virtual image magnified in size by a factor of three?
A) 33.3 mm B) 48.0 mm C) 38.3 mm D) 42.2 mm E) 54.4 mm
The excited state of a certain atom is 3.2 eV ± 0.21 eV. (h = 6.626 × 10-34 J ? s, 1eV = 1.60 × 10-19 J)
(a) What is the average lifetime of this state, in femtoseconds? (b) If the excited energy were doubled (to 6.4 eV ± 0.21 eV), how would the lifetime be affected?
Exclusion Principle: In a hydrogen atom, a given electron has n = 7. How many possible values can ? have?
A. 6 B. 7 C. 15 D. 98