Astronomers believe that most of the matter that makes up the universe is not detected by any part of the electromagnetic spectrum. This mysterious matter is called ______________
Fill in the blank(s) with correct word
dark matter
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Newton's Second Law in 2 Dimensions: A 1000-kg barge is being towed by means of two horizontal cables. One cable is pulling with a force of 80.0 N in a direction 30.0° west of north. In what direction should the second cable pull so that the barge will accelerate northward, if the force exerted by the cable is 120 N? Assume that the water exerts no appreciable frictional drag on the barge.
A. 19.5° east of north B. 21.1° east of north C. 39.0° east of north D. 47.5° east of north E. 54.7° east of north
In our Solar System, an object is called a planet if
A. it has cleared its neighborhood. B. it is spherical. C. it orbits the Sun. D. All of these choices are correct.
Whenever a gas is compressed,
A. heat must leave the gas. B. the temperature of the gas must get smaller. C. its internal energy must get smaller. D. work must be done on the gas.
Optical SETI is useful for
A) focused communication over short distances and in particular directions B) communication over wide areas and large distances C) communication over large distances in directions where interstellar dust is not present D) communication with civilizations which surround similar stars to our Sun and hence have evolved to see visible radiation