If sunlight were green instead of white, the most comfortable color to wear on a hot day would be
A) magenta.
B) yellow.
C) green.
D) blue.
E) violet.
Answer: C
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A journal bearing is idealized as a stationary flat plate and a moving flat plate that moves parallel to it. The space between the two plates is filled by an incompressible fluid. Consider such a bearing with the stationary and moving plates at 10°C and 20°C respectively, the distance between them is 3 mm, the speed of the moving plate is 5 m/s, and there is engine oil between the plates.
(a) Calculate the heat flux to the upper and lower plates
(b) Determine the maximum temperature of the oil.
GIVEN
Journal bearing: Two flat plates, one stationary, one moving with oil between them
Stationary plate temperature (Ts) = 10°C
Moving plate temperature (Tm) = 20°C
Distance between plate (H) = 3 mm = 0.003 m
Speed of the moving plate (Up) = 5 m/s
FIND
(a) Heat flux (q/A) for the plates
(b) The maximum temperature of the oil
ASSUMPTIONS
Steady state
Constant physical properties
Negligible edge effects
Oil is incompressible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 17, for engine oil at 15°C
Thermal conductivity (k) = 0.145 W/(m K)
Absolute viscosity (?) = 1.561 (Ns)/m2
Prandtl number (Pr) = 196
The most important property of a star which determines its evolution is its
A) chemical composition B) surface temperature C) mass D) radius
Why is it believed that the rings of Saturn could not have formed just as the planet itself formed?
a. Over time the solar wind should have blown away the particles in the rings. b. The particles in the rings should fall into the planet in a short period of time. c. The rings are made of ice particles which would have been vaporized by the heat released as Saturn formed. d. The outer planets do not have enough mass to hold on to the rings.
Estimate the speed of the Earth relative to the Sun in m/s
1.less than 0.003 2.between 0.003 and 0.03 3.between 0.03 and 0.3 4.between 0.3 and 3 5.between 3 and 30 6.between 30 and 300 7.between 300 and 3,000 8.between 3,000 and 30,000 9.more than 30,000 10.Impossible to determine