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Finding jumping height on an unknown planet given Mass/Radius

  1. Jul 30, 2012 #1
    1. The problem statement, all variables and given/known data
    Knowing you can jump about 1m high on Earth's surface, how high can you jump on the unknown planet.
    Munknown= 4.19*10^21kg
    Radius Unknown= 1*10^6m

    2. Relevant equations
    Not sure if can be used in this question
    K1+U1 = K2 + U2
    1/2MV2 + mgh = 1/2MV2 + mgh
    U=-GM/r and U = mgh
    g=GM/R2

    3. The attempt at a solution

    I found the force of gravity on the unknown planet using GM/R2
    Giving me 0.28m/s2
    Can I just equate the two equations for Gravitional Potential energy (U) to find the new height? as in -GM/r = mgh?
     
    Last edited: Jul 30, 2012
  2. jcsd
  3. Jul 30, 2012 #2
    If you were to do that, you are saying that the initial energy on each planet is the same.
    Is it?
     
  4. Jul 30, 2012 #3

    SammyS

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    How do the mass & radius of Planet X compare to those of Earth?

    Do you know Newton's law of universal gravitation ?

    Added in Edit:

    I see that you did add some information after I quoted the OP.
     
  5. Jul 30, 2012 #4
    Sorry I posted the question initially while I went and grabbed my work.
    Newtons universal law of gravitation...
    F=GM1M2/R2
    Though I don't know where I would use it.
    Am I on the right track using conservation of energy but instead of using mgh use -GM/r ?
     
  6. Jul 30, 2012 #5
    Well if we're considering the initial point to be grounded wouldn't the initial just be 0 on both planets? I'm lost as to how to relate Earth to the unknown
     
  7. Jul 30, 2012 #6
    Were does the energy that makes a person jump come from?

    Does this source maintain its full potential when transferred to a planet with different gravity?
     
  8. Jul 30, 2012 #7
    I think the energy stored in one's muscle must be the same everywhere.
     
  9. Jul 30, 2012 #8
    So...can someone tell me if this is correct?
    Since I know the gravitational potential energy (U) is mgh on earth. It gives me 490J assuming a mass of 50kg. I used the same equation U=mgh, solving for h gives: U/mg=h.
    Since the gravitational acceleration is GM/R2 the acceleration on the new planet is 0.28m/s2. I just plugged it in to give me a jump height of 35m.
     
  10. Jul 31, 2012 #9
    You can check about Apollo astronauts jumping on the surface of the moon.
    Conservation of energy applies everywhere.
     
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