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Homework Help: Weight On Mars - Please Help

  1. Feb 1, 2010 #1
    1. The problem statement, all variables and given/known data

    The problem is to find what 150lbs on earth = Xlbs on mars.

    2. Relevant equations


    G = 6.67x10^-11 (obviously)

    3. The attempt at a solution

    I'm getting incredibly annoyed because he gave us the wrong units etc, and we didn't even go over this in class. The last time I did this was in Highschool Physics...

    150lbs = 68KG

    mars has .108 the mass of Earth and the diameter is 6,787KM

    FG (W) = 6.67x10^-11 (68 KG) 6.45x10^23 KG
    ___________________________ = 8.63 newtons?...
    3393.5^2 KM

    I know my answer needs to be 249N which = 56lbs (I went onto an online calculator thing)
    Last edited: Feb 1, 2010
  2. jcsd
  3. Feb 1, 2010 #2


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    Check your units. Shouldn't you have the units of Mars' radius in meters? Make sure your units for G go with your other units.
  4. Feb 2, 2010 #3

    Doc Al

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    Staff: Mentor

    This might be easier to solve using ratios.

    [tex]F_e = \frac{GmM_e}{R_e^2}[/tex]

    [tex]F_m = \frac{GmM_m}{R_m^2}[/tex]

    Divide to find Fm/Fe. Doing it this way, several things cancel and you don't have to worry about converting units.
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