An ice skater has a moment of inertia of 5.0 kg ? m2 when her arms are outstretched, and at this time she is spinning at 3.0 rev/s. If she pulls in her arms and decreases her moment of inertia to 2.0 kg ? m2, how fast will she be spinning?
A) 7.5 rev/s B) 3.3 rev/s C) 10 rev/s D) 2.0 rev/s
A
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A non-conducting sphere of radius R = 7.0 cm carries a charge Q = 4.0 mC distributed uniformly throughout its volume. At what distance, measured from the center of the sphere, does the electric field reach a value equal to half its maximum value?
A) 3.5 cm only B) 4.9 cm only C) 3.5 cm and 9.9 cm D) 3.5 cm and 4.9 cm E) 9.9 cm only
A block attached to an ideal spring of spring constant 15 N/m executes simple harmonic motion on a frictionless horizontal surface
At time t = 0 s, the block has a displacement of -0.90 m, a velocity of -0.80 m/s, and an acceleration of +2.9 m/s2 . The mass of the block is closest to A) 2.3 kg B) 2.6 kg C) 4.7 kg D) 9.4 kg
What happens when the electron in a hydrogen atom flips its direction of spin, from parallel to anti parallel to that of the proton?
A. Nothing, this transition never occurs. B. The atom emits high-energy ultraviolet rays. C. The atom emits 656-nm radiation that gives red color. D. The atom emits 21-cm radio radiation.
Which of the following is the best answer to the question, "Why does the Sun shine?"
A) As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine. B) As the Sun was forming, nuclear fusion reactions in the shrinking clouds of gas slowly became stronger and stronger, until the Sun reached its current luminosity. C) The Sun initially began making energy through chemical reactions. These heated the interior enough to allow gravitational contraction and nuclear fusion to occur. D) The Sun initially began generating energy through nuclear fusion as it formed, but today it generates energy primarily through the sunspot cycle.