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Homework Help: ~Gravity on a distant planet

  1. Mar 13, 2008 #1
    1. The problem statement, all variables and given/known data
    You have been visiting a distant planet. Your measurements have determined that the planet's mass is twice that of earth but the free-fall acceleration at the surface is only one-fourth as large. Radius = 1.8*10^7meters
    Mass = 1.19484 × 10^25 kilograms


    2. Relevant equations
    U_g = -(G*M*m)/r
    v_escape = sqrt(2GM/r)

    3. The attempt at a solution

    I just plugged in the variables to the espace velocity equation and get 94km/s, but thats incorrect.
     
  2. jcsd
  3. Mar 13, 2008 #2
    The radius was given in the first part of the problem.
     
  4. Mar 13, 2008 #3

    Dick

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    Um. The radius and the mass are correct. But I get 9.4km/sec. Check the decimal point.
     
  5. Mar 13, 2008 #4

    Dick

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    g=G*M/r^2. It's force/mass not potential/mass.
     
  6. Mar 13, 2008 #5
    Yeah, looks like I was just being retarded
     
  7. Mar 13, 2008 #6

    Dick

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    S'ok. Reminds me of my post where I was strongly suggesting an OP integrate voltage over a gaussian surface to get enclosed charge. Duh.
     
  8. Mar 13, 2008 #7
    Lol, guess we all screw up sometimes :rofl:
     
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