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Homework Help: Universal gravitational, elliptical orbits

  1. Nov 18, 2009 #1
    1. The problem statement, all variables and given/known data
    a spacecraft of mass 1000kg, in an elliptical orbit about the earth, at one point its distance from earth is 1.2 x 107 meters and its velocity is 7.1 x 103 meters per sec, and the velocity vector is perpendicular to the line connecting the center of the earth to the spacecraft. Mass of earth is 6.0 x 1024 kg and radius of earth is 6.4 x 106
    Find the magnitude of the angular moemntum of the spacecraft about the center of the earth

    2. Relevant equations

    L = I [tex]\omega[/tex]
    L = r x p
    [tex]\omega[/tex] = v/r
    3. The attempt at a solution

    ok so I know that energy and angular momentum is conserved. I know how to solve this but I just want to make sure. Do I just do this by finding the angular velocity by [tex]\omega[/tex] = v/r then multiplied by I which equals to mr2 . it sounds really weird so I just want to make sure.
  2. jcsd
  3. Nov 18, 2009 #2


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    Just use L=rxp. What's the length of r, the length of p and the angle between them?
  4. Nov 18, 2009 #3
    I think it's mvr .. they didnt say anything about angle or anything. the velocity vector is perpendicular so it's sin 90 = 1 .
  5. Nov 18, 2009 #4


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    so you shoul have all the info for L = r x p, which becomes |L| = r(mv).sin(theta) = r(mv) = mvr, when the velocity & position vector are perpindicular
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