Which of the following contains the most energy per gram?
A. TNT
B. chocolate chip cookies
C. battery
D. uranium
Answer: D. uranium
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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
In order to understand star clusters, we need to be able to estimate their ages. What technique do scientists use for this?
A) radioisotope dating B) counting the planets that have formed around the largest stars C) finding the main-sequence turnoff point of the stars D) calculating orbital parameters using Kepler's Laws E) measuring its parallax
A 7.0-kg object is acted on by two forces. One of the forces is 10.0 N acting toward the east. Which of the following forces is the other force if the acceleration of the object is 1.0 m/s2 toward the east?
A) 6.0 N east B) 3.0 N west C) 12 N east D) 9.0 N west E) 7.0 N west
An electron of mass 9.11 × 10^-31 kg moves with a speed of 0.800c. What is its momentum? (c = 3.00 × 10^8 m/s)
a. 3.64 × 10^-22 kg×m/s c. 6.03 × 10^-22 kg×m/s b. 2.05 × 10^-22 kg×m/s d. 1.34 × 10^-22 kg×m/s