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    • Thread Starter

    I need help in this question... i am getting no where -

    consider the three dimensional motion of a planet about the sun. take the sun as the origin and let r=( x(t), y(t) , z(t) ) be the position vector of a planet at time t. show that the angular momentum L=mr x v of the planet about the sun is constant. show also that the planet moves in a plane containing the sun. (neglect the gravitational effects of other planets.)

    (Consider orbits of planets about the sun to be planar)

    If velocity is constant, then surely L is constant. For the second bit you're showing z(t)=constant, which I think must be a bit of differentiation.
    • Thread Starter

    which is getting to be too complicated...
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