What makes variable stars useful in determining star distances?
A. They are brighter than other stars.
B. Their exact location in the H-R diagram is known.
C. They are easier to spot than ordinary stars.
D. Their luminosity can be determined from their pulsation period.
Answer: D
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A long 0.6-m-OD 347 stainless steel (k = 14 W/(m K)) cylindrical billet at 16°C room temperature is placed in an oven where the temperature is 260°C. If the average heat transfer coefficient is 170 W/(m2 K), (a) estimate the time required for the center temperature to increase to 232°C by using the appropriate chart and (b) determine the instantaneous surface heat flux when the center temperature is 232°C. but assume that the billet is only 1.2-m-long and the average heat transfer coefficient at both ends is 136 W/(m2 K).
GIVEN
• A cylindrical billet placed in an over
• Billet outside diameter = 0.6 m
• Thermal conductivity (k) = 14 W/(m K)
• Initial temperature (To) = 16°C
• Oven temperature (T?) = 260°C
• The average heat transfer coefficient h cs = 170 W/(m2 K)
• Increase of the center temperature is 232°C
• Billet length (2L) = 1.2 m
• Heat transfer coefficient at the ends h ce = 136 W/(m2 K)
FIND
• The time required using the appropriate charts
ASSUMPTIONS
• Two dimensional conduction within the billet
• Constant and uniform thermal properties
• Constant oven temperature
SKETCH
We say that the Moon is gibbous when
A) it appears to be more than half illuminated, but not full. B) it appears to be less than half illuminated, but not new. C) it is exactly half illuminated. D) we see a thin crescent of light. E) the Moon is visible in the morning.
A temperature difference of 5 K is equal to
A. a difference of 9 on the Celsius scale. B. a difference of 9 on the Fahrenheit scale. C. a difference of 2.8 on the Rankine scale. D. a difference of 0.5 on the Fahrenheit scale. E. a difference of 2.8 on the Celsius scale.
Two objects of different mass are released simultaneously from the top of a 20-m tower and fall to the ground. If air resistance is negligible, which statement best applies?
a. The greater mass hits the ground first. b. Both objects hit the ground together. c. The smaller mass hits the ground first. d. No conclusion can be made with the information given.