In general, warm days are associated with
A) high surface pressure.
B) low surface pressure.
C) summer storms.
D) negative change in pressure gradient.
Answer: B
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Consider the electrical space heater, where the electric resistance heating coil is enclosed in a straight horizontal polished metallic cylinder that has an outer diameter of 1 cm and an emissivity of 0.9. If its surface temperature is at 110°C and the room air temperature is at 20°C, calculate the total heat loss per unit length of the cylinder due to both convection and radiation. For the purpose of this calculation, assume that the reflector is so designed that it “collects” all of the radiant heat from the back half of the horizontal heater and that it reflects 95% of the incident radiation.
GIVEN
• An electric resistance heating coil enclosed in horizontal metallic cylinder.
• Emissivity (?) = 0.9
• Diameter of cylinder (D) = 1 cm= 0.01 m
• Surface temperature (Ts) = 110°C= 383 K
• Ambient air temperature (T?) = 20°C= 293 K
• Reflects 95% of incident radiation.
FIND
Total heat loss per unit length of cylinder due to convection and radiation.
ASSUMPTIONS
• Air is still
• Surface temperature is uniform and constant
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 65°C
Thermal expansion coefficient (?) = 0.00296 1/K
Thermal conductivity (k) = 0.02825 W/(m K)
Kinematic viscosity (?) = 19.92 × 10–6 m2/s
Prandtl number (Pr) = 0.71
In the figure below, a disk (radius R = 1.0 m, mass = 2.0 kg) is suspended from a pivot a distance d = 0.25 m above its center of mass. For a circular disk, 
. The angular frequency (in rad/s) for small oscillations is approximately
?
?
A. 4.2. B. 2.1. C. 1.5. D. 1.0. E. 3.8.
The lunar mare are younger than any of the craters that sit in them
Indicate whether the statement is true or false
If the relative humidity is 50%, what happens when the temperature drops and the mass of water in the air stays the same?
A) Relative humidity drops. B) Relative humidity rises. C) Relative humidity stays the same. D) Outcome depends on the temperature of the air.