Homogeneity and isotropy, taken as assumptions regarding the structure and evolution of the universe, are known as:
A) Obler's Paradox.
B) Hubble's Law.
C) Wien's Law.
D) the Cosmological Principle.
E) the Grand Unified Theory.
D
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The shield of a nuclear reactor is idealized by a large 25 cm thick flat plate having a thermal conductivity of 3.5 W/(m K). Radiation from the interior of the reactor penetrates the shield and there produces heat generation that decreases exponentially from a value of 187.6 kW/ m3. at the inner surface to a value of 18.76 kW/m3 at a distance of 12.5 cm from the interior surface. If the exterior surface is kept at 38°C by forced convection, determine the temperature at the inner surface of the shield. Hint: First set up the differential equation for a system in which the heat generation rate varies according to (0)e–Cx
IVEN
Large flat plate with non-uniform internal heat generation Thickness (L) = 25 cm=0.25 m Thermal conductivity (k) = 3.5 W/(m K) Exterior surface temperature (To) = 38°C Heat generation is exponential with values of
? 187.6 kW/m3 at the inner surface
? 18.76 kW/m3 at 12.5 cm from the inner surface
FIND
The inner surface temperature (Ti)
ASSUMPTIONS
One dimensional, steady state conduction The thermal conductivity is constant No heat transfer at the inner surface of the shield
SKETCH
Spiral tracers tend to be old, luminous stars
a. True b. False Indicate whether the statement is true or false
In a location where the train tracks run parallel to a road, a high speed train traveling at 60 m/s passes a car traveling at 30 m/s in the opposite direction. How long does it take for the train to be 180 m away from the car?
a. 2.0 s b. 3.0 s c. 6.0 s d. 9.0 s e. 18.0 s
Which of the following pairs of atomic nuclei would feel the strongest repulsive electromagnetic force if you tried to push them together?
A) helium and helium B) hydrogen and hydrogen C) hydrogen and helium D) hydrogen and deuterium