Freely falling bodies experience
a. motion with constant velocity
b. motion with zero acceleration
c. motion with constant acceleration
d. motion at a constant speed
e. none of the above
C
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Spiral arms are obvious—easily-seen features—because they contain ____
a. dense molecular clouds b. atomic hydrogen clouds c. sun-like stars d. OB associations e. supernovae
Why is iron significant to understanding how a supernova occurs?
A) Iron is the heaviest of all atomic nuclei, and thus no heavier elements can be made. B) Supernovae often leave behind neutron stars, which are made mostly of iron. C) The fusion of iron into uranium is the reaction that drives a supernova explosion. D) Iron cannot release energy either by fission or fusion.
While the gondola is rising at a speed of 2.0 m/s, a passenger in a balloon-supported gondola throws a small ball down at a speed of 5.0 m/s relative to his body. A person who measures the ball's velocity at the instant of release will find that the ball's velocity relative to the ground at that instant is
A. 2.0 m/s, up. B. 3.0 m/s, down. C. 3.0 m/s, up. D. 5.0 m/s, down. E. 12.8 m/s, down.
The half-angle of the conical shock wave produced by a supersonic aircraft is 60°. What is the ratio of the speed of the aircraft to the speed of sound?
A) 2.0 B) 1.7 C) 0.87 D) 1.2