Radioactive Decay: One material used in nuclear bombs is 239Pu, with a half-life of 24,000 years. How long must we wait for a buried stockpile of this substance to decay to 1/1000 of its original activity?
A. 1,200,000 years
B. 240,000 years
C. 150,000 years
D. 82,000 years
E. 1500 years
Answer: B
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A BCC unit cell contains ______________lattice point(s).
Fill in the blank(s) with the appropriate word(s).
Suppose that, for some unknown reason, the core of the Sun suddenly became hotter. Which of the following best describes what would happen?
A) Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and turn the Sun into a giant star. B) Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal. C) Higher temperature would cause the rate of fusion to fall, decreasing the internal pressure and causing the core to collapse until the rate of fusion returned to normal. D) The higher temperature would not affect the fusion rate but would cause the core to expand and cool until the temperature returned to normal, with the core at a new, slightly larger size.
A basketball player jumps to make a basket, and remains in the air for a moment. A sportscaster, talking about the game, then remarks that she has "defied gravity." Which of the following accurately describes the situation?
A) The player did stay in the air in spite of the Law of Gravitation, but a single counter-observation is not enough to warrant revisiting a theory that usually works. B) The player produced enough force with her legs to accelerate up into the air, and gravity brought her back down with an acceleration of 9.8 m/s2. C) The player only seemed to defy gravity, but part of the Universal Law of Gravitation makes an exception for basketball players. D) The player has defied gravity, so scientists must go back into the lab to refine their theory.
How does Mercury's rotation relate to the Sun?
A) Its rotation rate is 2/3 as long as its year, due to tidal resonances. B) Its day is the same length as its year. C) Its year is much shorter, only 88 days, than its slow rotation of 243 days on its axis. D) It always keeps one face tidally locked toward the Sun, as our Moon does with us. E) It does not spin at all, being tidal stopped by the solar tides.