We should expect galaxies to collide fairly often because
a. they are large with respect to their separation distances.
b. galaxies contain large amounts of neutral hydrogen.
c. galaxies occur in clusters.
d. they are large with respect to their separation distances and galaxies occur in clusters.
e. None of the other choices are correct.
d
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What observation has prompted astronomers to ponder the possible existence of dark energy?
a. discovery of quasars b. discovery of superclusters c. supernovae appear fainter than expected at large redshifts d. uniform nature of the cosmic microwave background (CMB)
An ambulance is generating a siren sound at a frequency of 2,400 Hz. The velocity of sound is 345.0 m/s. If the ambulance is traveling at a velocity of 24.00 m/s toward the stationary observer, then what is the frequency of the siren perceived by the observer?
A. 2,579 Hz B. 2,540 Hz C. 2,525 Hz D. 2,500 Hz E. 2,480 Hz
Orion is visible on winter evenings in the northern hemisphere but not summer evenings because of
A) interference from the full Moon. B) the tilt of Earth's axis. C) the location of Earth in its orbit. D) the precession of Earth's axis. E) baseball on television.
What type of particle accelerator has two large D-shaped electrodes with a small gap between them, through which an alternating potential difference accelerates the particles in a constant magnetic field?
A) linear accelerator B) synchrotron C) cyclotron D) None of the above