The main sequence has a limit at the lower end because
a. low mass stars form from the interstellar medium very rarely.
b. low mass objects are composed primarily of solids, not gases.
c. pressure does not depend on temperature in degenerate matter.
d. the lower limit represents when the radius of the star would be zero.
e. there is a minimum temperature for hydrogen nuclear fusion (the definition of a star).
E
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This is negative throughout the region, therefore, T(y) is concave down throughout the region and the temperature at y = 1.6 mm is indeed the maximum temperature. These calculations are verified by the graph of T(y). Inserting ymax into the expression for T(y) yields: Tmax = T(0.00161 mm) = 48.8°C.
GIVEN
A journal bearing
Diameter (D) = 100 mm = 0.1 m
Clearance (H) = 0.5 mm = 0.0005 m
Rotational speed (@) = 3600 rpm
Oil properties
? Density (p) = 800 kg/m3
? Viscosity (?) = 0.01 kg/ms
? Thermal conductivity (k) = 0.14 W/(m K)
Temperature of bearing surface (Tb) = 60°C
FIND
(a) Temperature distribution in the oil film
ASSUMPTIONS
Steady state
Uniform and constant bearing surface temperature
Constant fluid properties
The journal surface is insulated (negligible heat transfer)
SKETCH
An astronaut is in equilibrium when he is positioned 140 km from the center of asteroid X and 581 km from the center of asteroid Y, along the straight line joining the centers of the asteroids. What is the ratio of the masses X/Y of the asteroids?
A) 0.0581 B) 17.2 C) 0.241 D) 4.15
Which is a useful property of a prism?
A) internally reflects 100% of incident light B) changes directions of light in a variety of ways C) re-inverts images D) all the above E) none of the above
A manufacturer in the U.S. wants to sell a refrigeration system to a customer in Germany. The standard measure of refrigeration capacity used in the United States is the ‘ton’; a one-ton capacity means that the unit is capable of making about one ton of ice per day or has a heat removal rate of 12,000 Btu/hr. The capacity of the American system is to be guaranteed at 3 tons. What would this guarantee be in SI units?
GIVEN - A three-ton refrigeration unit to be sold in Germany FIND (a) The rating in SI units