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Linear & Angular Quantities

  1. Nov 16, 2006 #1
    Electric toothbrushes can be effective in removing dental plaque. One model consists of a head 1.10 cm in diameter that rotates back and forth through a 70.0 degree angle 7600 times/min. The rim of the head contains a thin row of bristles.


    Part A: What is the average angular speed in each direction of the rotating head, in rad/sec?

    (140degrees)(pi/180) = 2.44 rad/rev

    w = (7600 rev/min)(1min/60sec)(2.44rad/1rev) = 310 rad/sec

    Part B What is the average linear speed in each direction of the bristles against the teeth?

    A little unsure of

    v = rw
    v = (.006m)(310rad/sec)
    v = 1.85 m/s
  2. jcsd
  3. Nov 16, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Your method looks OK. To avoid round-off errors in your arithmetic, don't round off until the very last step.
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