The critical density of the universe is the
A) average density the universe would need for gravity to someday halt the current expansion if dark energy did not exist.
B) actual average density of the universe.
C) density of dark matter in the universe.
D) density of water.
A
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The arrow in the photo on the left points to the location of the star that has exploded as a supernova in the photo on the right. From this photo pair alone, what can we conclude about the star that exploded? (Assume that we know the star was not a member of a binary system.)
A) It was a high-mass star with at least 8 times the mass of the Sun. B) It is now a black hole. C) It was a red giant star. D) Before the supernova, the star lived for at least a billion years.
In a series LRC circuit, the frequency at which the circuit is at resonance is f0. If you double the resistance, the inductance, the capacitance, and the voltage amplitude of the ac source, what is the new resonance frequency?
A) f0 B) f0/4 C) 2 f0 D) f0/2 E) 4 f0
Which of the following studies is best suited to astronomical observations that fall into the category called time monitoring?
A) studying how a star's brightness varies over a period of 3 years B) studying how different planets differ in their surface compositions C) measuring the rotation rate of a distant star D) determining the age of the solar system
Two mirrors are at right angles to one another. A light ray is incident on the first at an angle of 30°with respect to the normal to the surface. What is the angle of reflection from the second surface? ?
A. ?30° B. ?60° C. ?45° D. ?53° E. ?75°