What is the meaning of the term "critical mass"?
A)
This refers to the mass of the "critical" elements in a reactor, i.e., the uranium or plutonium.
B)
This refers to the minimum amount of fissionable material required to sustain a chain reaction.
C)
This refers to the maximum amount of fissionable material required to sustain a chain reaction.
D)
This is the amount of mass needed to make a power reactor economically feasible.
E)
This is the material which is just on the verge of becoming radioactive.
B
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A distance R away from a light source we observe which of the following for the electromagnetic field it produces?
A) Both the light intensity and the magnitude of the electric field drop as 1/R2. B) The light intensity drops as 1/R2, but the magnitude of the electric field drops as 1/R. C) Both the light intensity and the magnitude of the electric field drop as 1/R. D) The light intensity drops as 1/R, but the magnitude of the electric field drops as 1/R2. E) None of the previous answers is correct.
The observed evidence we have for black holes includes
A) X-rays that are thought to come from the center of a black hole. B) visible light that is thought to come from the center of a black hole. C) temperature measurement of certain extremely cold stars that are thought to be black holes. D) X-rays that are thought to come from gases that are outside of a black hole. E) observations of certain regions of space, larger than the largest known stars, that emit no light.
Rocks are grouped into three classes depending on how the rock was
A) formed. B) located. C) discovered. D) shaped.
Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest
A) right after the object is released. B) at the top of its trajectory. C) The acceleration of the object is the same throughout the entire trajectory.