The center of a long uniform log is raised to shoulder level while the other end is on the ground. If instead, the end of the log is raised to shoulder level, the work required is
A) half.
B) the same.
C) twice.
Answer: A
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A thermocouple (0.8-mm-OD) is located horizontally in a large enclosure whose walls are at 37°C. The enclosure is filled with a transparent quiescent gas that has the same properties as air. The electromotive force (emf) of the thermocouple indicates a temperature of 230°C. Estimate the true gas temperature if the emissivity of the thermocouple is 0.8.
GIVEN
• Horizontal thermocouple in a large enclosure
• Thermocouple outside diameter (D) = 0.8 mm = 0.0008 m
• Enclosure wall temperature (Te) = 37°C = 310 K
• Gas is enclosure is quiescent and has the same properties as air
• Thermocouple reading (Ttc) = 230°C = 503 K
• Thermocouple emissivity (?) = 0.8
FIND
• True gas temperature (T?)
ASSUMPTIONS
• Enclosure behaves as a black body
• Conduction along the thermocouple out of the enclosure is negligible
SKETCH
PROPERTIES AND CONSTANTS
The Stephan-Boltzmann Constant (?) = 5.67 ?10–8 W/(m2 K4).
When a charged particle is moved along an electric field line,
a. the electric field does no work on the charge. b. the electrical potential energy of the charge does not change. c. the electrical potential energy of the charge undergoes the maximum change in magnitude. d. the voltage changes, but there is no change in electrical potential energy. e. the electrical potential energy undergoes the maximum change, but there is no change in voltage.
A cylindrical tank is assembled by welding steel sections in a helical pattern with angle ? 5 50°. Tank diameter is 1.6 m, thickness is 20 mm, and internal pressure is 2.75 MPa. Modulus E 5 210 GPa and Poisson’s ratio ? 5 0.28. The circumferential strain in the wall of the tank is approximately:
(A) 1.9 3 1024
(B) 3.2 3 1024
(C) 3.9 3 1024
(D) 4.5 3 1024
The fundamental nuclear reaction occurring in the core of the Sun is ________
A) nuclear fusion of helium into carbon B) nuclear fusion of hydrogen into helium C) radioactive decay D) nuclear fission