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Applications of circular motion and gravitation

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On a planet with no atmosphere and a mass twice that of Earth's, a 12.5kg rock falls off of a cliff. Beginning at an arbitrary time during free fall, the resulting vertical velocity of the rock as a function of time is shown in the graph.
Determine the radius of this planet in terms of Earth radii, RE.
Write your answer to two significant figures.
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi