What fraction of the Galaxy's mass is in a form that does not emit electromagnetic radiation?
A. about 90%
B. about 10%
C. about 50%
D. Zero percent; all of the Galaxy emits some form of light.
Answer: A
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Conduction: Two metal rods, one silver and the other copper, are both immersed at one end in a steam chamber at a temperature of 100°C. The other end of each one is in an ice water bath at 0°C. The rods are 5.0 cm long and have a square cross-section that is 2.0 cm on a side. No heat is exchanged between the rods and the surroundings, except at the ends. How much total heat flows through the two rods each minute? The thermal conductivity of silver is 417 W/m ? K, and that of copper is 395 W/m ? K.
A. 20 kJ B. 39 kJ C. 47 kJ D. 49 kJ E. 11 kJ
How is the Mars Rover mission different from Global Surveyor mapping mission?
What will be an ideal response?
Multiple-Object Accelerating Systems: Two boxes P and Q on a perfectly smooth horizontal surface are connected by a light horizontal cord. The mass of P is greater than that of Q. A horizontal force 
is applied to box Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P is
A. zero. B. less than F but not zero. C. equal to F. D. greater than F.
Stromatolites are
A) fossils of the first organisms to introduce oxygen into the atmosphere B) fossils of the first multicellular organisms C) layers of sediment that once contained colonies of ancient microbes D) fossils of the first eukaryotes