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Homework Help: Kapler's orbits

  1. Dec 24, 2009 #1
    In question 3(b) in the following file
    http://phstudy.technion.ac.il/~wn114101/hw/wn2010_hw09.pdf [Broken]

    Why the orbit will be a straight line?
    I think that when the particles are coming to r=0 the potential will be infinity, isn't that so?
    So the energy will be infinity and e will be infinity... please help me...
    thank you

    AND ONE MORE THING: if the potential is a/r^2 (>0) then then the two objects will attract each other, right? But in the Gravitational law (-Gm1m2/r^2) the potential is <0 and the objects will attract to each other
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Dec 30, 2009 #2


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    The problem statement explicitly states the particles move "on the x direction" and "on the y direction". Presumably they mean on the x and y axes; it is not worded quite properly but I can't imagine it meaning anything else.

    So, each particle moves in straight line simply because the problem statement says that they do. What would actually cause this to happen is not important.

    No, it would be negative infinity in this example.
    Last edited by a moderator: May 4, 2017
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