A particle moves along the x axis. The slope of the arrow representing an object’s four-momentum on an energy–momentum diagram is equal to
A. The particle’s speed.
B. The particle’s x-velocity.
C. The inverse of the particle’s speed.
D. The inverse of the particle’s x-velocity.
E. The particle’s energy.
D. The inverse of the particle’s x-velocity.
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A semiconductor with an electrical conductivity of 300 (?·m)-1 at room temperature is produced by doping Group IV silicon with Group V antimony. Assume that the mobility of electrons in silicon is equal to 0.10 m2 /V·s and that the mobility of holes is equal to 0.001 m2 /V·s. You can assume that this semiconductor is in the extrinsic range of operation at this temperature.
(a) What type of semiconductor is this? (b) What doping concentration of antimony in atoms/m3 is necessary for this electrical conductivity? (c) State clearly any assumptions you make in this calculation.
Elastic Collisions: In the figure showing an isolated system, determine the character of the collision. The masses of the blocks, and the velocities before and after, are shown. The collision is
A. perfectly elastic. B. partially inelastic. C. completely inelastic. D. characterized by an increase in kinetic energy. E. not possible because momentum is not conserved.
Two harmonic waves are described by 
What is the magnitude of the speed (in m/s) of the two traveling waves?
A. 16 B. 4.0 C. 8.0 D. 0.25 E. 2.0
Suppose we could magically triple the distance between Earth and the moon. This would cause the gravitational force by Earth on the moon to be
A) increased to three times its former value. B) be unchanged. C) reduced to 1/4 of its former value. D) reduced to 1/3 of its former value. E) reduced to 1/9 of its former value.