How do astronomers know that the nuclei of some galaxies are active?
a. Their nuclei are much brighter than expected.
b. The orbits of stars near the center of the galactic nuclei are faster than expected.
c. The luminosity of the nuclei varies over time.
d. The color of the nuclei is different than expected.
C
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A small 175-g ball on the end of a light string is revolving uniformly on a frictionless surface in a horizontal circle of diameter 1.0 m
The ball makes 2.0 revolutions every 1.0 s. (a) What are the magnitude and direction of the acceleration of the ball? (b) Find the tension in the string.
One of the first large organisms to develop the means to live on land were probably
A) plants B) insects C) reptiles D) mammals
Electromagnetic radiation of wavelength 3.5 meters is which type?
A) AM-radio B) microwaves C) FM-radio D) visible E) ultraviolet
The moons of Mars are ______________; that is, they always keep the same face toward the planet
Fill in the blank(s) with correct word