According to current theory, which of the following elementary particles does not contain quarks?
A. Protons
B. Electrons
C. Mesons
D. Neutrons
Answer: B
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One result of bombardment of the Moon's surface is a layer of broken, pulverized, and powdered rock called
A. regolith. B. maria. C. lunar rays. D. basalt.
Percival Lowell’s claims of a Martian civilization generated great public interest, but other scientists of his time were highly skeptical of these claims. Which two of the following statements (which are all true) explain why other scientists of the late 19th and early 20th centuries rejected Lowell’s claims?
a. Lowell’s canals did not appear in photographs of Mars taken through telescopes. b. Lowell’s canals followed perfectly straight lines for thousands of kilometers. c. Mars has an axis tilt very similar to Earth’s axis tilt. d. Like Earth, Mars has polar ice caps. e. Mars rotates with a period only a little longer than Earth’s rotation period.
A uniform, horizontal beam of length 6.0 m and weight 140 N is attached at one end to a wall by a pin connection (so that it may rotate). A cable attached to the wall above the pin supports the opposite end. The cable makes an angle of 60° with the horizontal. What is the tension in the cable needed to maintain the beam in equilibrium?
a. 81 N c. 70 N b. 69 N d. 140 N
Spiral galaxies have more gas, dust, and younger stars than elliptical galaxies do
Indicate whether the statement is true or false