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Homework Help: Mechanical Energy

  1. Mar 9, 2007 #1
    1. The problem statement, all variables and given/known data

    Zero, a hypothetical planet, has a mass of 1.0x10^23 kg, a radius of 3.0x10^6 m, and no atmosphere. A 10 kg space probe is to be launched vertically from its surface.
    (a) If the probe is launched with an initial kinetic energy of 5.0x10^7 J, what will be its kinetic energy when it is 4.0x10^6 m from the center of Zero?

    2. Relevant equations

    (1/2)mv^2 - (GMm/R)=(1/2)mv^2 - (GMm)/(10R)

    3. The attempt at a solution

    5.0e7 - [(6.67e-11)(1e23)(10)]/(3e6)= KE - [(6.67e-11)(1e23)(10)]/(10(4e6)]

    I don't think that I am using the right values for R though. Am I???
     
  2. jcsd
  3. Mar 9, 2007 #2

    Mentz114

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    Gold Member

    I can't see where the 10R comes from. Should be R as on the LHS.
     
  4. Mar 9, 2007 #3
    ok, well do I have the correct values of R set up in the equation or do I need to take the difference of the distance of the satellite to the center or anything?
     
  5. Mar 10, 2007 #4

    Mentz114

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    Gold Member

    I think all your distances are measured from the centre of Zero.
     
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