The site from which an airplane takes off is the origin. The x axis points east; the y axis points straight up. The position and velocity vectors of the plane at a later time are given by
?
and 
m/s.
?
The plane is most likely
A. just touching down.
B. in level flight in the air.
C. ascending.
D. descending.
E. taking off.
Answer: B
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Earth doesn't experience a solar eclipse every month because
a. of unpredictable weather patterns. b. the Moon always keeps its same side toward the Earth. c. the Moon's orbit plane is not aligned with the Earth's orbit plane. d. its sometimes nighttime when the eclipse occurs. e. sometimes the Moon is too far away.
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.
LR Circuits: As shown in the figure, a circuit consists of a resistor R = 18 ? in series with an ideal inductor L = 33 H having no resistance. At time t = 0 s, there is a 12-A current in the circuit. When the magnetic energy of the inductor is 1600 J, what is the rate of dissipation of energy in the resistor?
A. 1700 W B. 440 W C. 870 W D. 1300 W E. 2200 W
A protostar becomes a main sequence star when it ________.
A. starts fusing helium B. starts glowing with infrared light C. starts fusing hydrogen to helium D. starts fusing heavier elements