What is the galactic fountain model?
A) the idea that there is a lot of interstellar water vapor
B) the theory that the Milky Way is a spiral galaxy and looks like a whirlpool from above
C) the theory that hot, ionized gas blows out of the galactic center like a jet or fountain
D) the theory that hot, ionized gas blown out of the galactic disk and into the halo by superbubbles cools down and falls back into the disk
E) none of the above
D
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Equilibrium: A 400-kg box is lifted vertically upward with constant velocity by means of two cables pulling at 40.0° on either side of the vertical direction. What is the tension in each cable?
A. 231 N B. 400 N C. 800 N D. 2560 N E. 3920 N
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Answer the following statement true (T) or false (F)
What evidence do astronomers have that the Universe is expanding?
A. There is a measurable redshift in the spectral lines of distant galaxies. B. Galaxies disappear when they pass the cosmic horizon. C. The disks of galaxies are getting smaller over time. D. Nearby clusters of galaxies are smaller than more distant ones. E. Distant galaxies are dispersing, pulled apart by the expansion of space.
Captain Jirk reports to headquarters that he left the planet Senesca 1.88 × 104 seconds earlier. Headquarters sends back the message: "Was that spaceship proper time?" It will be spaceship proper time if it was
A. measured by one clock fixed at one spot on Senesca. B. measured by one clock fixed at one spot on the spaceship. C. measured by a clock on Senesca at departure and by a clock on the spaceship when reporting. D. measured by a clock on the spaceship when departing and by a clock on Senesca when reporting. E. calculated by dividing the distance from Senesca according to Senesca by the speed of the spaceship.