A radioactive isotope has a half-life of one month. At the end of one month, the amount of the original isotope still remaining is
1) none,
2) one-quarter,
3) one-half,
4) three-fourths,
and at the end of two months, the amount of original isotope remaining is
5) none.
6) one-fourth.
7) one-half.
8) three-fourths.
Answer: 3, 6
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A) x-ray binary systems that lie close to the galactic center B) massive-star supernovae near the galactic center C) comet-sized objects being torn apart by the tidal forces of the black hole near the galactic center D) supernova shock waves plowing into dense regions of the interstellar medium near the galactic center
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Fill in the blank(s) with correct word
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When you blow some air above the upper face of a paper strip, the paper rises. This occurs because
A) the air above the upper face of the paper moves faster, which makes the pressure lower than at the lower face. B) the air above the upper face of the paper moves faster, which makes the pressure higher than at the lower face. C) the air above the upper face of the paper moves slower, which makes the pressure lower than at the lower face. D) the air above the upper face of the paper moves faster but the pressure remains constant. E) the air above the upper face of the paper moves slower, which makes the pressure higher than at the lower face.