Density waves may explain:
A) the lack of blue stars in the halo.
B) the random orbits of halo stars.
C) the density of red stars in the bulge.
D) the spiral arm structure of the Galaxy.
E) the large number of open clusters in the halo.
D
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A particle with charge Q is on the y axis a distance a from the origin and a particle with charge q is on the x axis a distance d from the origin. The value of d for which the x component of the force on the second particle is the greatest is:
A) 0 B) a C) sqrt(2a) D) a/2 E) a/sqrt(2)
Bats can detect small objects such as insects that are of a size on the order of a wavelength. If bats emit a chirp at a frequency of 60 kHz and the speed of soundwaves in air is 330 m/s, what is the smallest size insect they can detect?
A. 1.5 mm B. 3.5 mm C. 5.5 mm D. 7.5 mm E. 9.8 mm
The end of the cutting cord on a gas-powered weed cutter is 0.21 m in length. If the motor rotates at the rate of 20 rev/s, what is the tangential speed of the end of the cord?
a. 13 m/s b. 4.2 m/s c. 26 m/s d. 2.7 m/s
Stalactites are
a. Rocks solidified from molten material below ground. b. Consolidated sediment deposited in layers. c. Dripstone formations that form on cavern floors. d. Dripstone formations that form on cavern ceilings.