A white dwarf is:
A) supported by energy flowing outward from its core.
B) formed when low-mass stars are born.
C) responsible for the conversion of thermal energy into gravitational energy.
D) unable to generate energy by nuclear fusion.
D
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How do the atmospheres of the Moon and Mercury compare?
A) Mercury's is much denser, like Venus, with much carbon dioxide. B) They are about equal, each only 1% as dense as ours. C) The cooler Moon retains a thicker nitrogen atmosphere. D) As no spacecraft has yet landed there, no information exists about Mercury's. E) Neither body has a permanent true atmosphere.
If you pitch a baseball with twice the kinetic energy you gave it in a previous pitch, the magnitude of its momentum is
A) 4 times as much. B) 2 times as much. C) doubled. D) times as much. E) the same.
A charged particle (mass = M, charge = Q > 0) moves in a region of space where the magnetic field has a constant magnitude of B and a downward direction. What is the magnetic force on the particle at an instant when it is moving horizontally toward the north with a speed V?
a. QVB toward the east b. Zero c. QVB toward the west d. QVB upward e. QVB toward the south
A metal plate is placed in the sunlight. The incident radiant energy G is 780 W/m2. The air and the surroundings are at 10°C. The heat transfer coefficient by natural convection from the upper surface of the plate is 17 W/(m2 K). The plate has an average emissivity of 0.9 at solar wavelengths and 0.1 at long wavelengths. Neglecting conduction losses on the lower surface, determine the equilibrium temperature of the plate.
GIVEN
- A metal plate is sunlight
- Incident radiant energy
- Temperature of air and surroundings
- Natural convection heat transfer coefficient
- Plate emissivity (?) = 0.9 at solar wavelengths, 0.1 at long wavelengths
FIND
-The equilibrium temperature of the plate (Tp)
ASSUMPTIONS
- Steady state
- Conduction losses on the lower surface of the plate are negligible
- The surroundings behave as a blackbody enclosure
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
