Relative to a stationary observer, a moving object
A)
appears shorter than normal.
B)
appears longer than normal.
C)
keeps its same length.
D)
can do any of the above. It depends on the relative velocity between the observer and the object.
E)
can do any of the above. It depends on the relative energy between the observer and the object.
A
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A 3-m-long steel rod (k = 43 W/(mK), ? = 1.17 × 10–5 m2/s) is initially at 20°C and insulated completely except for its end faces. One end is suddenly exposed to the flow of combustion gases at 1000°C through a heat transfer coefficient of 250 W/(m2 K) and the other end is held at 20°C. How long does it take for the exposed end to reach 700°C? How much energy will the rod have absorbed if it is circular in cross section and has a diameter of 3 cm?
GIVEN • Steel rod with one end at fixed temperature and the other end exposed to combustion gases FIND (a) Time required for the exposed face to reach 700°C (b) Heat input to the rod
All the following statements about Mars are true. Which one might have led to a significant loss of atmospheric gas to space?
A) Mars lost any global magnetic field that it may once have had. B) The axis tilt of Mars is thought to change significantly with time. C) Outgassed water molecules are split apart, and the oxygen then reacts chemically with surface rock on Mars. D) Mars probably once had a much higher density of greenhouse gases in its atmosphere than it does today.
Lenz's Law: A coil lies flat on a tabletop in a region where the magnetic field vector points straight up. The magnetic field vanishes suddenly. When viewed from above, what is the sense of the induced current in this coil as the field fades?
A. The induced current flows counterclockwise. B. The induced current flows clockwise. C. There is no induced current in this coil. D. The current flows clockwise initially, and then it flows counterclockwise before stopping.
The quantity volt is equivalent to which of the following?
a. J/C c. J×C b. C/W d. J×m