All the following statements are true. Which one explains why convection can occur in the troposphere but not in the stratosphere?
A) Temperature declines with altitude in the troposphere but increases with altitude in the stratosphere.
B) Atmospheric pressure is much greater in the troposphere than in the stratosphere.
C) The stratosphere contains significant amounts of ozone but the troposphere does not.
D) Clouds tend to form in the troposphere but not the stratosphere.
A) Temperature declines with altitude in the troposphere but increases with altitude in the stratosphere.
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Carnot Engine: An ideal Carnot engine is operated between a hot and a cold reservoir. The temperature difference between the two reservoirs is 284°C. If the efficiency of this ideal engine is 24.0%, find the temperature of the cold reservoir in degrees Celsius.
Fill in the blank(s) with the appropriate word(s).
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
As you walk away from a plane mirror on a wall, the height of your image
A) is always the same size. B) is always a real image, no matter how far you are from the mirror. C) gets smaller. D) changes from being a virtual image to a real image as you pass the focal point. E) may or may not get smaller, depending on where the observer is positioned.
The two strongest forces that act between protons in a nucleus are
A) the weak nuclear and electromagnetic forces. B) the weak nuclear and the gravitational forces. C) the electrostatic and the gravitational forces. D) the strong nuclear and the electrostatic forces.