What is the celestial equator?
A) another name for the ecliptic
B) the path the Sun appears to trace through the constellations each year
C) a projection of Earth's equator into space
D) the technical name of the Sun's equator
C) a projection of Earth's equator into space
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A circular ice skating rink, 20 m in diameter, is enclosed by a large hemispherical dome of diameter 30 m. Assuming that the ice is 2 cm thick, estimate the time it takes for the ice to melt if the refrigeration system of the rink fails. Make this calculation first with both the dome and the ice behaving as black bodies at respective temperatures of 20°C and 0°C. Then repeat with the water-ice having an emissivity of 0.3 and losing heat by natural convection to the air in the dome with a convection heat transfer coefficient of 15 W/(m2 K).
GIVEN
• Circular skating rink enclosed by hemispherical dome
• Diameter of the rink (D1) = 20 m
• Diameter of hemispherical dome (D2)= 30 m
• Temperature of dome and surrounding air (T2)= 200C
• Temperature of ice (T1) = 00C
FIND
Time it takes for ice to melt if the refrigeration system of rink fails considering (a) both dome and ice behaving as black bodies. (b) ice having emissivity of 0.3 and loosing heat by natural convection to air in dome with 2 15 W/(m K)
SKETCH
PROPERTIES AND CONSTANTS
Latent Stefan-Boltzman’s heat of fusion constant for ice (Lf)= (? 334 KJ/kg )=5.67*10-8 W/(m2 K4)
What is Eris?
A) an icy object that orbits in the Kuiper belt and is more massive than Pluto B) the largest known asteroid C) a moon of Pluto D) an extrasolar planet ejected by another solar system and captured by ours
Roughly how far across is the Milky Way?
A. 10 million light-years B. 25,000 light-years C. 25 light-years D. 100,000 light-years
When a charged particle is moved along an electric field line,
a. the electric field does no work on the charge. b. the electrical potential energy of the charge does not change. c. the electrical potential energy of the charge undergoes the maximum change in magnitude. d. the voltage changes, but there is no change in electrical potential energy. e. the electrical potential energy undergoes the maximum change, but there is no change in voltage.