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Homework Help: Laser experiment, determine angular velocity

  1. Aug 16, 2013 #1
    1. The problem statement, all variables and given/known data

    A circular cannister of some reflective liquid is spinning at some ω. The distance between the cannister and the surface is given by

    h(r) = h(0) + (ω2/2g)r2

    Where g ≈ 9.82 and r is the distance to the axis of revolution. When we shine two parallell laser beams on the surface, we find that they meet at a point 22 cm above the surface.

    Find ω.

    2. Relevant equations

    f = R/2

    3. The attempt at a solution

    We have a parabolic mirror with radius of curvature = 0.44 m. But I'm not really sure how to find the equation for a parabola given the curvature. I was well on my way to taking the gradient of the parabola and setting up some kind of system of vector equations, but I suspect that would be overkill...
  2. jcsd
  3. Aug 16, 2013 #2
    Figured it out.
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