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Calculating Gravitational Potential

  1. Jun 3, 2015 #1
    1. The problem statement, all variables and given/known data:
    "Calculate gravitational potential at point Z, which is 8.10 x 107m away from a planet of mass 1.08 x 1023. "

    (This point is between the planet and a moon, where the gravitational field strength is zero. I'm not sure if that makes a difference. The moon's mass is 4.8 x 1022 and point Z is 5.4 x 107m away from it.).

    2. Relevant equations
    V = - G M / r


    3. The attempt at a solution
    V = - (6.67 x 10^-11) x (1.08 x 10^23) / (8.1 x 10^7)
    Therefore
    V = - 8.89 x 10^4 J/kg

    Is this correct?

    Many thanks in advance.

    - Talli
     
  2. jcsd
  3. Jun 3, 2015 #2

    PeroK

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    Why can you ignore the gravity of the moon?
     
  4. Jun 3, 2015 #3
    Whoops! Sorry moon. Does this mean I calculate V for both the planet and the moon, and add the two?

    So for the moon...
    V = - (6.67 x 1011) x (4.8 x 1022) / (5.4 x 107)
    V = - 5.93 x 104
     
  5. Jun 3, 2015 #4

    PeroK

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    Yes. It's good that you wanted to add them and not subtract them!
     
  6. Jun 3, 2015 #5
    Wonderful! I won't say I didn't consider it for a minute... But that would imply one field disappears with the presence of another, so no!

    So VPlanet + Vmoon:
    - 5.93 x 104 + - 8.89 x 107 = - 1.429 x 108

    Thanks so much for your help. :smile:
     
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