Spiral arms are obvious—easily-seen features—because they contain ____
a. dense molecular clouds
b. atomic hydrogen clouds
c. sun-like stars
d. OB associations
e. supernovae
d
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Radioactivity Basics: In the radioactive decay equation 
Po? ? 
Po + X, what is X?
Fill in the blank(s) with the appropriate word(s).
An s state (l = 0 ) energy level is split into two levels by an applied magnetic field. A photon of microwave radiation having frequency 60 GHz induces a transition between the two levels
What is the magnitude of the applied magnetic field? (h = 6.626 × 10-34 J ? s, Bohr magneton = ?B = 9.27 × 10-24 J/T) A) 0.34 T B) 2.1 T C) 1.2 T D) 2.8 T E) 13 T
A railroad freight car, mass 15,000 kg, is allowed to coast along a level track at a speed of 2.0 m/s. It collides and couples with a 60,000-kg loaded second car, initially at rest and with brakes released. What percentage of the initial kinetic energy of the 15,000-kg car is preserved in the two-coupled cars after collision?
a. 20% c. 86% b. 23% d. 100%
The south pole of a bar magnet is moved toward a short helical coil of wire (solenoid) along the axis of the coil. The coil has 100 turns and the ends of the coil are connected to form a closed circuit. If the coil is replaced with a single loop of the same type of wire, and the magnet is moved exactly as before, the current induced in the loop is
A. zero in both cases. B. 100 times larger. C. 100 times smaller. D. the same as in the coil.