What use are 21 cm radio waves to Galactic astronomers?
A) They cut through the dusty cocoons to let us watch star birth.
B) We can reflect them off the core of the Galaxy.
C) Their Doppler shifts let us map the motions and locations of gas in the spiral arms.
D) They bounce off stars like our Sun to let us precisely measure their distances.
E) They pick up the cool, dark matter much better than can optical telescopes.
C
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A 2.00 kg mass is attached to a spring with a spring constant of 48.0 N/m. If the maximum speed of the mass in this system is 1.14 m/s, what is the energy of the quanta of energy in this system?
A) 2.23 × 10-34 J B) 6.63 J C) 6.63 × 10-34 J D) 5.17 J E) 5.17 × 10-34 J
In an RLC series circuit, if the AC frequency is increased to a very large value, what value does the phase angle between the current and voltage approach?
a. 90° b. 0° c. –90° d. 45°
Fourier discovered that music can be
A) a series of non-periodic waves. B) reduced to simple sine waves. C) a binary code. D) pulses of the same amplitude.
A 4,000 kg satellite is traveling in a circular orbit 200 km above the surface of the Earth. A 3.00 gram marble is dropped inside the satellite. What is the force of gravity on the marble as viewed by the observers on the Earth? 
A. 0.405 N B. 0.362 N C. 0.277 N D. 0.202 N E. 0.185 N