The period from about one to 100 seconds after the Big Bang is called the:
A) pair-production era.
B) atomic epoch.
C) nuclear epoch.
D) quark epoch.
E) lepton epoch.
E
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Binary (double) stars can be detected by
a. being seen as two separate stars with a telescope. b. one star traveling a wiggly proper-motion path across the sky. c. one star dimming abruptly as another passes in front of it. d. pairs of absorption lines seen in the spectrum of what appears to be one star. e. All of the other choices are correct.
A hollow steel ball of diameter 3.0 m barely floats in water. What is the thickness of the wall of the ball? The density of iron is 7.87 g/cm3 and that of water is 1000 kg/cc
A) 6.6 cm B) 37 cm C) 131 cm D) 79 cm
If a force always acts perpendicular to an object's direction of motion, that force cannot change the object's kinetic energy
A) True B) False
Suppose a current-carrying wire has a cross-sectional area that gradually becomes smaller along the wire so that the wire has the shape of a very long, truncated cone. How does the drift speed vary along the wire?
1.It slows down as the cross section becomes smaller. 2.It speeds up as the cross section becomes smaller. 3.It doesn't change. 4.More information is needed.