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Homework Help: Conceptual problem: Finding gravitational KE

  1. Nov 17, 2008 #1
    1. The problem statement, all variables and given/known data

    to find KE of an orbiting body, do I use 1/2mv^2 or 1/2Gm1m2/r??

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Nov 17, 2008 #2


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    Homework Helper

    Hi grantP,

    If it's a circular orbit (for example) then it would just depend on which is more convenient for the problem.
  4. Nov 19, 2008 #3
    For an orbiting body, gravitational force provides for the centripetal force:

    mv2/r = GMm/r2

    0.5mv2 = 0.5GMm/r

    Just to digress abit, so the total energy an orbiting body with distance r away from the centre of the planet is:

    KE + GPE = 0.5GMm/r + (-GMm/r)

    = -0.5GMm/r
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