Galaxies that are far away from us have spectra that are redshifted more than galaxies that are closer to us. It is thought that the reason for this is that
A. the stars in more distant galaxies are older and cooler than those nearby.
B. we are at the center of an expanding universe.
C. we are at the edge of the universe and moving away from the center.
D. space itself is expanding.
Answer: D
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A. 0.79 m/s2 B. 0.87 m/s2 C. 0.95 m/s2 D. 1.0 m/s2
A leaf falls from a tree. Compare its kinetic energy K to its potential energy U
A) K increases, and U decreases. B) K decreases, and U increases. C) K decreases, and U decreases. D) K increases, and U increases. E) K and U remain constant.
On Earth, according to current ideas about plate tectonics, ____________ were once together
a. Africa and South America b. Africa and North America c. North America and Europe d. Africa and South America; Africa and North America; and North American and Europe
) Based on observations, which of the following statements about stars in the Milky Way is generally true?
A) the older the star, the lower its abundance of heavy elements B) the older the star, the bluer its color C) the older the star, the faster its orbital speed D) the younger the star, the higher its mass E) the less massive the star, the older it is