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Homework Help: A question on gravity

  1. Oct 26, 2015 #1
    • Moved from technical forums. Did not use template.
    I have seen a question about two bodies left in a free space and the question ask when shall they collapse.
    For solving this I reached this step:(GM)*r^-2)*dr=(M*(m+M)^-1)*v*dv
    For the left side,the lower bound of the integral is R and the upper bound is 0.after calculating it the answer of the left side is:1*0^-1-(GM*R^-2),what can we do with it?
  2. jcsd
  3. Oct 26, 2015 #2


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    Hi Sobi, welcome to PF :smile: !

    Interesting question, but assume that I don't know how you got here. Could you tell a little more about what you started with, what steps you did to get here ?
  4. Oct 26, 2015 #3
  5. Oct 26, 2015 #4

    Vanadium 50

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    Are we going to have to wring this out of you one line at a time? "Could you tell a little more about what you started with, what steps you did to get here?" was a very good question, and pretty much what we need to know to help you.
  6. Oct 26, 2015 #5
    Continuing the question:I then multiplex the right side of it with dr*dr^-1.then bringing dt to the left side of the equation then it became the integral I talked about first.
  7. Oct 27, 2015 #6
    Can someone answer my question
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