To melt ice, add
A) temperature.
B) energy.
C) force.
D) time.
Answer: B
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Suppose a satellite orbits the earth so closely that it experiences some drag due to the earth’s upper atmosphere. This will drain away some of the orbital energy of this system, converting it to thermal energy. If this happens fairly slowly, the satellite’s orbit will remain nearly circular. What happens to the radius of this satellite’s orbit as time passes in this case?
A. It slowly decreases. B. It remains the same: just the satellite’s speed decreases. C. It slowly increases
According to current understanding, how did the first generation of stars differ from stars born today?
A) They contained much more hydrogen and helium than stars born today. B) They were much cooler in temperature than most stars born today. C) They were much more likely to be members of binary star systems than stars are born today. D) They were much more massive than most stars born today.
Consider three galaxies, Alpha, Beta and Gamma. An astronomer in Beta sees each of the other two galaxies moving away from her in opposite directions at 0.70c
At what speed would an observer in Alpha see the galaxy Beta moving? A) 0.82c B) 0.70c C) 0.94c D) 0.35c E) 0.57c
Recently, superconducting wire was made using magnesium diboride (S. Jin, H. Mavoori, C. Bower, and R. B. Van Dover, "High critical currents in iron-clad superconducting MgB2 wires," Nature 411, 563 (2001))
This is assumed to hold the promise of cheap efficient energy transmission. Explain how this might be true.