Which of the following is not associated with a cold front?
A) thunderstorms
B) drop in air pressure
C) gradually rising warm air
D) clear skies behind the front
Answer: C
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What happens to light passing through even thin clouds of dust?
A) The light that passes through them is blueshifted due to the cloud's approach. B) Its motion causes all light to be redshifted as it passes through these clouds. C) Its motion causes the light of stars beyond to twinkle. D) Even a little can completely block all light, such as the Horsehead Nebula. E) It dims and reddens the light of all more distant stars.
An 100-g piece of copper, initially at 295°C, is dropped into 250 g of water contained in a 300-g aluminum calorimeter; the water and calorimeter are initially at 10.0°C. What is the final temperature of the system? (Specific heats of copper and aluminum are 0.0920 and 0.215 cal/g•°C, respectively. cw = 1.00 cal/g•°C)
a. 12.8°C c. 18.1°C b. 16.5°C d. 32.1°C
A long cylinder of 0.1-m-diameter has a surface temperature of 400 K. If it is immersed in a fluid at 350 K, natural convection will occur as a result of the temperature difference. Calculate the Grashof and Rayleigh numbers that will determine the Nusselt number if the fluid is
(a) Nitrogen
(b) Air
(c) Water
(d) Oil
(e) Mercury
GIVEN
• A long cylinder immersed in fluid
• Diameter (D) = 0.1 m
• Surface temperature (Ts) = 400 K
• Fluid temperature (T?) = 350 K
FIND
The Grashof number (Gr) and the Rayleigh number (Ra) if the fluid is
(a) Nitrogen (b) Air (c) Water (d) Oil (e) Mercury
ASSUMPTIONS
• The cylinder is in a horizontal position (the characteristic length is the diameter of the cylinder)
SKETCH
PROPERTIES AND CONSTANTS
The thermal expansion coefficients for oil and mercury can be estimated from
Earth is closest to the Sun in January and farthest from the Sun in July. Compare the number of seconds in an Earth day for these two months