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Homework Help: Orbits and gravitacional field

  1. Feb 20, 2006 #1
    considering a Planet 1 and a Planet 2, where 1 is extremly heavier than 2 and 2 is going in Planet 1's orbit. Two questions

    1) howto get the expression v = - G m2 m1 / r

    2) if we consider the energy < 0, we can get to an expression as
    v < sqrt (2GM2 / r)

    howto get Vx and Vy for that V ?

    (r is the radius.)

    Hints and other help are welcome. Thanks.
  2. jcsd
  3. Feb 20, 2006 #2


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    The 'v' in this expression is potential energy. It's just the intergal of F= Gm1m2 / r^2.

    Some of your other 'v's look like they might be velocity.
  4. Feb 20, 2006 #3
    Oh... that's why couldn't get a Velocity experssion like that.

    The second is for velocity, taken from the mecanical energy expression and using e<0. So since velocity is a vector, v = vx + vy and we have an expression for the scalar value of v, how can we get each of the components? This is necessary for setting up the initial values in a simulation program.

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