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Homework Help: Centre of mass problem

  1. Dec 9, 2013 #1
    1. The problem statement, all variables and given/known data

    Two objects of mass m=3kg and M=7kg are held at a distance of 10 meter in space and then released. They move towards each other due to mutual gravitation attraction. Determine the location of their meeting of the object mass m

    2. Relevant equations

    r= mr1+ Mr2/m+M

    3. The attempt at a solution
    The objects will meet at their center of their mass. What I am finding difficult to understand is the method of finding out r1 and r2 with respect to m from the given information
  2. jcsd
  3. Dec 9, 2013 #2

    Simon Bridge

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    You have two variables r1 and r2 ... so you need two equations.
    The other one is r=r1+r2
  4. Dec 11, 2013 #3
    We really don't know the value of r which means there are actually three variables. I have tried to solve it by using your method but 2 equations won't suffice in this case. We need one more equation
  5. Dec 11, 2013 #4
    You can find the center of mass using the equation:


    Take as x = 0 as the initial location of mass m.
  6. Dec 11, 2013 #5
    You mean I should take r1=0 @Chestermiller
  7. Dec 11, 2013 #6
    Yeah, although it doesn't really matter. Take the origin anywhere you want. The answer will come out the same (in terms of the distances from each of the two masses).
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