Two 5000-kg rail cars roll without friction (one at 1 m/s, the other at 2 m/s) toward each other on a level track. They collide, couple, and roll together with a combined momentum of
A) zero.
B) 5000 kg m/s.
C) 10,000 kg m/s.
D) 15,000 kg m/s.
Answer: B
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Which of the statements below is part of both the Ptolemaic and Copernican models?
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A watch dial that continues to glow after a week in the dark is almost certainly
A) fluorescent. B) phosphorescent. C) polarized. D) radioactive.
Long-period comets are believed to come from ______________
a. the Oort cloud b. interstellar space c. the asteroid belt d. the Great Red Spot
An inventor claims to have designed a perpetual motion machine, a device that creates its own power. Which of the following laws best explains why a perpetual motion machine cannot work?
A) Law of conservation of energy B) Law of conservation of matter C) Newton's second law D) Newton's third law