General Questions: The figure shows two boxes, with m1 > m2, that are on a level frictionless surface. We can apply a horizontal force 
either toward the right on m1 or toward the left on m2. The magnitude of the force that the boxes exert on each other is
A. zero newtons in either case.
B. larger if 
is applied toward the right.
C. larger if 
is applied toward the left.
D. the same in either case.
Answer: C
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Winds are generated on Earth primarily because of
a. strong updrafts from the equator and air sinking near the poles. b. uneven heating of the surface and rotation of the planet. c. water condensation onto mountains. d. hot air rising and cool air sinking.
Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit?
A) Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit. B) White dwarfs get hotter with increasing mass, and above the 1.4-solar-mass limit they would be so hot that even their electrons would melt. C) White dwarfs are made only from stars that have masses less than the 1.4-solar-mass limit. D) The upper limit to a white dwarf's mass is something we have learned from observations, but no one knows why this limit exists.
Suppose a planet with mass M has a moon with mass M. Where is the system’s center of mass? Refer to the diagram below. 
A. A B. B C. C D. D E. E
A segment of wire carries a current of 25 A along the x axis from x = ?2.0 m to x = 0 and then along the z axis from z = 0 to z = 3.0m. In this region of space, the magnetic field is equal to 40 mT in the positive z direction. What is the magnitude of the force on this segment of wire?
A. 1.0 N B. 5.0 N C. 2.0 N D. 3.6 N E. 3.0 N