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Homework Help: A question that asks you to figure out the mass of the moon

  1. Jan 25, 2012 #1
    1. The problem statement, all variables and given/known data

    the radius of the moon is 1 over 3.65 of the radius of the earth, while the acceleration due to gravity of the moon is 1 over 6 of that on the earth`s surface. calculate the mass of the moon.
  2. jcsd
  3. Jan 25, 2012 #2


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    Homework Helper

    The acceleration due to gravity - we call it g on Earth - is given by GM/R2. Where G is the universal constant of gravitation; M is the mass of the central body; and R is the distance form the centre of mass - the radius of the body if we consider g on the surface. You know sufficient of those values to calculate the mass of the Moon as a fraction of the mass of the Earth, which is a value that can be looked up easily.
  4. Jan 25, 2012 #3
    i thought you could figure out the mass of the moon without knowing the mass of the earth. tomorrow i have an exam and my teacher said don`t expect me to give you any sheet with equations and constants. so i guess i got to memorize the mass of the earth.
    thank you
  5. Jan 25, 2012 #4
    a = GM/R2

    g = (1/6)(9.81) = X m/s2

    r = (1/3.65)(6.378x106) = Y m

    m/r2 = a/G

    m/(Y)2 = X/ (6.67x10-11)

    m = ANS kg
  6. Jan 25, 2012 #5
    the person asking for help is supposed to set up the problem, give relevant equations etc. before getting help from outside. Where are your equations??

    In answer to your question - you do have to know the formulas probably but not the mass of the earth.
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