Over 99.9% of dry air at sea level is composed of the gases N2, O2, and ______________
Fill in the blank(s) with correct word
Ar
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In fission bombs, a certain "critical mass" is needed because
A) the fissionable material will not reach a sufficiently high temperature unless this much material is present. B) if the mass is too small, too many neutrons pass through the uranium and out the sides without hitting a nucleus. C) too small an amount of uranium will not hold together throughout the reaction, and thus the uranium falls apart and the reaction goes out before it is completed. D) it is impossible to fission a uranium nucleus unless it is near a large number of other uranium nuclei. E) for smaller masses the pressure is so low that neutrons move too slowly through the uranium to sustain a chain reaction.
If the mass of the earth and all objects on it were suddenly doubled, but the size remained the same, the acceleration due to gravity at the surface would become
A) 4 times what it now is. B) 1/4 of what it now is. C) 2 times what it now is. D) the same as it now is. E) 1/2 of what it now is.
Scientists hope that some day they will be able to produce a theory which will combine the strong force, the weak nuclear force, and electromagnetism. This theory has been called
A) The Grand Unified Theory. B) The Theory of Everything. C) The Unified Field Theory. D) The Electroweak Theory. E) The Electrostrong Theory.
The tail of a comet always points
A) away from the Sun and becomes longest and brightest at perihelion. B) toward Earth and never varies. C) away from the Sun and disappears at perihelion. D) toward the Sun and disappears at perihelion. E) in the direction of the comet's motion.