Pluto's composition is most similar to that of a
A) terrestrial planet.
B) comet.
C) star.
D) jovian planet.
B) comet.
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Force on a Wire: A vertical wire carries a current straight up in a region where the magnetic field vector points toward the north. What is the direction of the magnetic force on this wire?
A. downward B. toward the north C. toward the east D. toward the west E. upward F. toward the south
The windings of a motor have a resistance of 4.0 ?. The counter emf of this motor when connected to a 120-V line and running at full speed is 104 V
(a) What is the start up current of this motor? (b) What is the current in the motor when running at full speed?
The natural circulation of water—from ocean to air to ground to ocean and then back to the atmosphere—is called the
A) circle of life. B) hydrologic cycle. C) carbon cycle. D) rock cycle.
Reconsider the problem of cooling of a rotating rod (shaft) by natural convection described in Example 8.6. Determine the shaft rotation at which the heat transfer contribution due to the rotation convection is about the same as that due to natural convection, and calculate the total heat transfer rate at this condition. Also, graph the variation of q, as well as its two components (qr and qnc) with shaft rpm ranging from 3 rpm to 15 rpm, and comment upon the results.
GIVEN
? Cooling of rotational shaft by natural convection
? Rod diameter (D) = 20 cm = 0.2 m
? Air temperature (T?) = 20°C
? Temperature of rotating rod (Tb) = 1000°C
FIND
? Shaft rotation at which heat transfer contribution due to rotational convection is same as that due
to natural convection.
? Total heat transfer rate at this condition.
? Graph of variation of q and qr and qnc with shaft rpm.
ASSUMPTIONS
? Radiation is negligible
? The shaft is horizontal
PROPERTIES AND CONSTANTS
