Venus is 95 percent the diameter of Earth
a. True
b. False
Indicate whether the statement is true or false
True
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A spherical satellite circling the sun is to be maintained at a temperature of 25°C. The satellite rotates continuously and is covered partly with solar cells having a gray surface with an absorptivity of 0.1. The rest of the sphere is to be covered by a special coating which has an absorptivity of 0.8 for solar radiation and an emissivity of 0.2 for the emitted radiation. Estimate the portion of the surface of the sphere which can be covered by solar cells. The solar irradiation may be assumed to be 1,420 W/m2 of surface perpendicular to the rays of the sun.
GIVEN
- A spherical satellite partially covered with solar cells is orbiting the sun
- Satellite temperature (Ts) = 25°C = 298 K
- Solar cell absorptivity (?c) = 0.1
- Absorptivity of the rest of the satellite (?2s) = 0.8
- Emissivity of the rest of the satellite (?s) = 0.2
FIND
The portion of the surface which can be covered by solar cells
ASSUMPTIONS
Ambient temperature (T?) = 0 K
Quasi steady state
Solar irradiation (Iso1) = 1420 W/m2 of the surface perpendicular to the rays of the sun
Satellite and cell surfaces are gray
Surface temperature of the satellite is uniform
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
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On the earth, when an astronaut throws a 0.250-kg stone vertically upward, it returns to his hand a time T later. On planet X he finds that, under the same circumstances, the stone returns to his hand in 2T
In both cases, he throws the stone with the same initial velocity and it feels negligible air resistance. The acceleration due to gravity on planet X (in terms of g) is A) g/4. B) g/2. C) g/ . D) g . E) 2g.
Calculate the Earth's angular momentum in the approximation that treats the Earth's orbit around the Sun as a circle. (MSun = 1.99 × 10^30 kg; T = 3.156 × 10^7 s; ME = 5.98 × 10^24 kg.)