The drag on a blunt object is due primarily to:
(A) The relatively high pressure on the front of the object
(B) The wake region
(C) The shear stress acting on the front and rear of the object
(D) The separated region
(D) The separated region
Even on a streamlined object, there is a relatively high pressure on the front. The wake does not exist except downstream of an object so it doesn’t account for the drag. It is the existence of a separated region in which a relatively low pressure combined with the relatively high pressure over the front that results in the drag.
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Two transparent materials are in contact. The one on the left has a lower index of refraction than the one on the right (nL A. The transmitted wave is unaffected and the reflected wave in inverted.
B. The transmitted wave is inverted and the reflected wave in unaffected.
C. Both the transmitted and reflected waves are inverted.
D. Both the transmitted and reflected waves are unaffected.
Which of the following is the most convincing observation that suggests that like Europa, Ganymede may also have a subsurface ocean?
A) the detection of salts on the surface that may have been brought up from below the crust B) the presence of young grooved terrain that may be the result of cryovolcanism C) the fact that it is the largest moon in the solar system and, hence, should have plenty of internal heat to maintain liquid water beneath its surface D) in addition to its internal magnetic field, Ganymede has a magnetic field induced by Jupiter which is consistent with a salty ocean beneath its crust
If R1 < R2 < R3, and if these resistors are connected in series in a circuit, which one dissipates the greatest power?
a. R1 c. R2 b. R3 d. All are equal in power dissipation.
Air at an average temperature of 150°C flows through a short square duct 10 × 10 × 2.25 cm at a rate of 15 kg/h. The duct wall temperature is 430°C. Determine the average heat transfer coefficient, using the duct equation with appropriate L/D correction. Compare your results with flow-over-flat-plate relations.
GIVEN
• Air flowing through a short square duct
• Average air temperature (Ta) = 150°C
• Duct dimensions = 10 × 10 × 2.25 cm = 0.1 × 0.1× 0.0225 m
• Duct wall surface temperature (Ts) = 430°C
• Mass flow rate (m ) = 15 kg/h
FIND
The average heat transfer coefficient ( h c) using (a) The duct equation with appropriate L/D correction (b) The flow-over-flat-plate relation
ASSUMPTIONS
• Constant and uniform duct wall temperature
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the average temperature of 150°C
Thermal conductivity (k) = 0.0339 W/(m K)
Absolute viscosity (?b) = 23.683 × 10–6 (Ns)/m2
Prandtl number (Pr) = 0.71 At the surface temperature of 430°C,
the absolute viscosity (?s) = 33.66 × 10–6