What evidence supports the theory that there is a black hole at the center of our galaxy?
A) We observe an extremely bright X-ray source at the center of our galaxy.
B) We can see gas falling into an accretion disk and central mass at the center of our galaxy.
C) The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across.
D) We observe a large, dark object that absorbs all light at the center of our galaxy.
E) all of the above
C
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Replacing a wire resistor with another of the same material and length but with three times the diameter will have the effect of changing the resistance by what factor?
a. 1/3 b. 1/9 c. 3 d. 9
A spaceship is observed by a stationary observer to be moving at 0.600 c. A laser beam is shown straight ahead from the front of the spaceship. How fast does the laser beam travel relative to the observer?
A. 1.60 c B. 1.36 c C. 1.00 c D. 0.640 c E. 0.360 c
A runner generates 1260 W of thermal energy. If this heat has to be removed only by evaporation, how much water does this runner lose in 15 minutes of running? The latent heat of vaporization of water is 22.6 × 105 J/kg
A) 40 g B) 35 g C) 350 g D) 500 g E) 50 g
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.