A radioactive material initially is observed to have an activity of 1000 decays/sec. If nine hours later it is observed to have an activity of 125 decays/s, what is its half-life?
a. 1/2 hour
c. 3 hours
b. 8 hours
d. 1 hour
C
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The light reflected from a soap bubble (n = 1.40) appears red (l = 640 nm) at its center. What is the minimum thickness (in nm)?
a. 124 b. 104 c. 114 d. 134 e. 234
Match the words in the left-hand column to the appropriate blanks in the sentences in the right-hand column. Use each word only once.
Saturn, Earth, Mars, Venus, Uranus, Mercury, Jupiter, Neptune
1. ____________ has a rotational axis that is tilted so much it lies nearly in the plane of its orbit.
2. ____________ is the planet with the highest average surface temperature.
3. The planet that orbits closest to the Sun is __________.
4. The only rocky planet to have more than one moon is ___________.
5. ___________ is the jovian planet that orbits closest to the Sun.
6. Most of the surface of _________ is covered with liquid water.
7. ___________ is about 30 times as far from the Sun as our own planet.
8. The planet with the lowest average density is ___________.
In a situation where an object can move only along the x axis, you see this statement in a book: “The object’s velocity is v = (x ? x0) / t, where x is the object’s position at time t to the left or right of its position x0 at time t = 0.” Is being used here as a shorthand for 
(A) or vx (C)?
A. A B. C
Which of the following is NOT a true statement about the relationship between the thermal expansion of a solid and the potential energy of an ion in a solid?