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How high does a rocket have to go above the earth's surface until its weight is 0.4 t

  1. Sep 28, 2007 #1
    how high does a rocket have to go above the earth's surface until its weight is 0.4 times its weight on the Earth's surface ? The radius of the earth is 6.37 * 10 ^ 6m and the acceleration of gravity is 9.8 m/s^2. Answer in units of km.

    what i got so far, i need help proceeding:

    Applying the inverse-square law:

    Final weight = 0.4 g = (1/2.5) g

    The square root of 2.5 = 1.581

    im stuck here, thanks :)
     
  2. jcsd
  3. Sep 28, 2007 #2

    arildno

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    ???????

    Wherever have used or set up the inverse square law?
     
  4. Sep 29, 2007 #3

    Mentz114

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    weight on surface = G*m*M/radius^2

    0.4*weight on surface = G*m*M/x^2

    Solve for x.
     
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