A particular material has an index of refraction of 2.75 . What percent of the speed of light in vacuum is the speed of light in the material?
a. 36%
b. 10%
c. 8%
d. 89%
a
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The stars farther than 20 000 LY from the center of the Milky Way are traveling too fast to be bound to the galaxy by the observed mass of the galaxy. Which of the following are currently being investigated as possible explanations of this?
a. neutrino mass b. WIMPs c. Newtonian dynamics are not quite correct. d. all of the above
A kid slides down an icy (frictionless) hill starting from rest. At the top his gravitational potential energy is 500 J.He slides part way down the hill to a point where his gravitational potential energy is 200 J. His kinetic energy at that point will be
a. 200 J. b. 300 J. c. some unknown value between 0 and 500 J. d. none of the above.
Two equal forces are applied to a door. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force exerts the greater torque?
A) the first at the midpoint B) the second at the doorknob C) both exert equal non-zero torques D) both exert zero torques E) Additional information is needed.
What is the celestial sphere?
A. Earth B. an observatory dome C. the Sun D. the imaginary sphere of the sky, on which stars lie