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Polar Coordinates Angular velocity

  1. Feb 6, 2008 #1
    1. The problem statement, all variables and given/known data
    A cameraman standing at A is following the movement of a race car traveling at a speed of 30 m/s. Determine the angular rate (theta dot) at which the man must turn to keep the camera directed on the car at theta = 30 degrees.

    b = 20 m
    a = 20 m
    theta = 30 degs
    2. Relevant equations

    vr = r dot
    vtheta = r*theta dot

    3. The attempt at a solution

    If only I knew r dot, I could figure this problem out.
    I found r with the law of cosines (r = 34.641 m).
    I was thinking of using
    30 = sqrt( (rdot)^2 + r^2(thetadot)^2)
    but I don't know r dot... where can I find the rate of change in r?
  2. jcsd
  3. Feb 6, 2008 #2


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    Science Advisor
    Homework Helper

    Change in r only depends on change in phi which is constant and very easy to work out in terms of b. You can write r in terms of a and b.
    So you can easily (he says!) write theta dot in terms of only a and b
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