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Homework Help: Kinetic energy of space probe problem

  1. Apr 22, 2007 #1
    1. The problem statement, all variables and given/known data
    Planet Zero has a mass of 4.0*10^23 kg and a radius of 2.0*10^6 m . With what kinetic energy should a 10-kg space probe be launched vertically from the surface of Zero so as to achieve a maximum distance of 4.0*10^6 m from Zero's center?

    3. The attempt at a solution
    I found the initial potential Energy, U=(GMm/radius planet Zero) and then the mecahnical energy at the end, E= - (GMm/2d)

    its not right..HELP!!!
  2. jcsd
  3. Apr 22, 2007 #2


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    Homework Helper

    I think most likely you are not using the right values for the distance.

    The question is effective asking for the difference in gravitational potential of two configurations, and they are:

    1. The space probe on the surface of this planet (distance of 2.0x10^6 from center)
    2. The space probe at a distance off the surface (distance of 4.0x10^6 from the center)

    Try doing the calculations carefully again.
  4. Apr 22, 2007 #3


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    Homework Helper

    How do you know it isn't right? What did you get for your final value? Be careful of your signs.
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