Communications satellites are synchronous satellites that orbit Earth each
A. 90 minutes
B. 24 hours
C. 28 days
D. They don't orbit Earth, they just stay in one place.
Answer: B. 24 hours
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To measure the mass flow rate of a fluid in a laminar flow through a circular pipe, a hot wire type velocity meter is placed in the center of the pipe. Assuming that the measuring station is far from the entrance of the pipe, the velocity distribution is parabolic where Umax is the centerline velocity (r = 0), r is the radial distance from the pipe centerline, D is the pipe diameter.
(a) Derive an expression for the average fluid velocity at the cross-section in terms of
Umax and D.
(b) Obtain an expression for the mass flow rate.
(c) If the fluid is mercury at 30°C, D = 10 cm, and the measured value of Umax is 0.2
cm/s, calculate the mass flow rate from the measurement.
GIVEN
• Fully developed flow of mercury through a circular pipe
• Parabolic velocity distribution: u(r)/Umax = 1 – (2r/D)2
• Mercury temperature (T) = 30°C
• Pipe diameter (D) = 10 cm = 0.1 m
• Measured center velocity (Umax) = 0.2 cm/s = 0.002 m/s
FIND (a) An expression for the average fluid velocity (u )
(b) An expression for the mass flow rate (m )
c) The value of the mass flow rate (m )
SKETCH
The density of interstellar dust is very low, yet it still blocks starlight because:
A) it is so cold it absorbs higher energy photons. B) there is 100 times more opaque gas than dust present in the ISM. C) the dust particles are about the same size as the light waves they absorb. D) the dust particles are irregular in shape. E) ice particles reflect all light back toward their stars, not toward us.
Neither heat nor work are state functions
Indicate whether the statement is true or false
The piston of a cylinder containing a quantity of ideal gas is advanced so that the volume of the gas is decreased by one-half. A pressure gauge on the cylinder shows the pressure of the gas to have increased threefold in the process. By what factor does the temperature of the gas change?