A 3rd magnitude star appears 2.5 times brighter than a 4th magnitude star
Indicate whether the statement is true or false
TRUE
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The average Reynolds number for air passing in turbulent flow over a 2-m-long flat plate is 2.4 x 106. Under these conditions, the average Nusselt number was found to be equal to 4150. Determine the average heat transfer coefficient for an oil having thermal properties similar to those in Appendix 2, Table 18 at 30°C at the same Reynolds number and flowing over the same plate.
GIVEN
Turbulent flow of air over a flat plate
Average Reynolds number (ReL) = 2.4 x 106
Plate length (L) = 2 m
Average Nusselt number (Nu) = 4150
FIND
Average heat transfer coefficient
ASSUMPTIONS
Steady state
Fully developed turbulent flow
Transition from laminar to turbulent flow occurs at Rex = 5 x 105
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 18, for oil at 30°C
Thermal Conductivity (k) = 0.11 W/(m K)
Kinematic Viscosity (v) = 15.4 ? 10–6 m2/s
Thermal Diffusivity (a) = 707 ? 10–10 m2/s
Hubble's constant is related to the age of the universe, but the precise relationship depends on the way in which the expansion rate changes with time. For a given value of Hubble's constant (such as 22 km/s/Mly), the age of the universe is oldest if
A) the expansion rate has been increasing with time (an accelerating universe). B) the expansion rate has remained nearly constant with time (a coasting universe). C) the expansion rate slows ever more gradually with time (a critical universe). D) the expansion rate is slowing enough that it will eventually reverse (a recollapsing universe).
Which of the following four objects has the greatest kinetic energy?
a. An object of mass m moving with speed 4v b. An object of mass 3m moving with speed 2v c. An object of mass 4m moving with speed v d. An object of mass 2m moving with speed 3v e. None of these; all four objects have the same kinetic energy.
Early astronomers believed that Earth did not move because they saw no ____, the apparent motion of an object because of the motion of the observer
a. uniform circular motion b. archeoastronomy c. heliocentrism d. eccentricity e. parallax