Radiant energy from the Sun reaches the Earth at a rate of 
When 30% of the radiant energy is reflected and 70% absorbed, the average temperature of the Earth's atmosphere is 253 K or -20
If the atmosphere absorbed 100% of the solar radiant energy, then what is the average temperature of the Earth's atmosphere?
A. 2.5
B. 2.8
C. 3.0
D. 3.6
E. 4.6
D. 3.6
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Reconsider the problem of cooling of a rotating rod (shaft) by natural convection described in Example 8.6. Determine the shaft rotation at which the heat transfer contribution due to the rotation convection is about the same as that due to natural convection, and calculate the total heat transfer rate at this condition. Also, graph the variation of q, as well as its two components (qr and qnc) with shaft rpm ranging from 3 rpm to 15 rpm, and comment upon the results.
GIVEN
? Cooling of rotational shaft by natural convection
? Rod diameter (D) = 20 cm = 0.2 m
? Air temperature (T?) = 20°C
? Temperature of rotating rod (Tb) = 1000°C
FIND
? Shaft rotation at which heat transfer contribution due to rotational convection is same as that due
to natural convection.
? Total heat transfer rate at this condition.
? Graph of variation of q and qr and qnc with shaft rpm.
ASSUMPTIONS
? Radiation is negligible
? The shaft is horizontal
PROPERTIES AND CONSTANTS
Which font in the figure above is an example of a serif font?
A. Tahoma B. Georgia C. Ravie D. Courier New
The angular momentum of a system remains constant
A) when the total kinetic energy is constant. B) when no net external force acts on the system. C) when the linear momentum and the energy are constant. D) when no torque acts on the system. E) all the time since it is a conserved quantity.
If you are asked to make a very sensitive glass thermometer, which of the following working fluids would you choose?
1.mercury 2.alcohol 3.gasoline 4.glycerin