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Homework Help: Angular Speed of a comet

  1. Nov 17, 2009 #1
    1. The problem statement, all variables and given/known data

    (a) A certain comet of mass m at its closest approach to the Sun is observed to be at a distance r1 from the center of the Sun, moving with speed v1. At a later time the comet is observed to be at a distance r2 from the center of the Sun, and the angle between rvec2 and the velocity vector is measured to be θ. What is v2?

    2. Relevant equations

    3. The attempt at a solution

    I thought it would be mv1cos(90-theta). But it's counting that wrong, and I only have one more attempt at this problem, and I'm not sure how to approach it.
  2. jcsd
  3. Nov 17, 2009 #2


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    Angular momentum is conserved, so find expressions for the angular momentum at the two points and set them equal.
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