A heat pump uses 200 J of work to output 300 J of heat into a heat reservoir at 200 K. What is the coefficient of performance for the heat pump?
A. 1.0
B. 1.5
C. 2.5
D. 2.8
B. 1.5
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Which galaxies contain less than 1,000 galaxies?
a. obtuse b. middle class c. poor d. rich
A sphere is constructed of two concentric pieces. The inner part is a solid sphere of radius 10.0 cm made of a material with density 4000 kg/m3
The outer part is a spherical shell with inner radius 10.0 cm and outer radius 20.0 cm. The outer shell has a density 9000 kg/m3. (a) What is the mass of this sphere? (b) What is the average density of this sphere?
In the greenhouse effect, what is the direct cause of extra heating of the Earth's surface?
A) Additional carbon dioxide makes the atmosphere more transparent to infrared light, allowing the sun to more directly heat the surface. B) Additional carbon dioxide makes the atmosphere more opaque to infrared light, trapping more of the infrared light emitted by Earth. C) Additional carbon dioxide makes the atmosphere more dense, so heat passes through it more slowly. D) Additional carbon dioxide makes the atmosphere emit more infrared light which gets trapped near the surface of the Earth.
Why is Mars red?
A) Chemical reactions between surface rock and atmospheric oxygen literally rusted the surface. B) Martian volcanoes released a much redder lava than volcanoes on Earth. C) The red color of Mars is a result of the scattering of light in the Martian sky. D) The red color is caused by water ice chemically bound in surface rock.