Suppose the half-life of some element is 2 days. If you purchase 10 grams of the element (which was produced in a laboratory 4 days ago), how much of this element would you have 3 days after you purchased it?
A) more than 2.5 grams but less than 5 grams
B) 2.5 grams
C) more than 1.25 grams but less than 2.5 grams
D) 1.25 grams
E) less than 1.25 grams
C
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Why does the Moon have a layer of powdery "soil" on its surface?
A) Large impacts shattered lunar rock to make this soil. B) The soil exists because the Moon accreted from powdery material after a giant impact blasted Earth. C) Volatiles escaping from the Moon's interior bubble upward and make the soil. D) The soil is the result of the same processes that make powdery sand on Earth. E) It's the result of gradual erosion by micrometeorites striking the Moon.
The ________ is determined by the distance that ________ can travel in a time span equal to the age of the Universe.
A. cosmological constant; neutrinos B. event horizon; light C. recession velocity; galaxies D. cosmic horizon; light
Which of the following is NOT a property of elliptical galaxies?
A. They have little dust or cold gas. B. They have prominent spiral arms. C. They contain mostly old (Pop II) stars. D. Stars are distributed smoothly throughout their volume.
What is the speed of light in a material that has an index of refraction of 2.0?
A. 
B. 
C. 
D. 
E. No such index can exist.