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Homework Help: Circular motion

  1. Jan 25, 2006 #1
    What I'm doing seems like it should work, but I can't seem to get it right. I'm sure I'm doing the math right, but I have a feeling I'm answering something that's not being asked. I would just like some help on setting up the equation right.

    A car starts from rest on a flat circular track of radius 200.1 m and accelerates tangentially at a rate of 4.79 m/s2. How much time elapses before the centripetal acceleration of the car is equal in magnitude to the tangential acceleration.

    I have the tangential acceleration (at), and radius (r).
    Using the centripetal acceleration equation ac=v2/r, I set ac=4.79 m/s2, r=200.1m, and solve for the velocity.

    I then use the circular motion period equation (v=(2*pi*r)/t), plug in the velocity I just calculated, the radius of the track, and solve for time.

    I get 40.61s everytime, which is incorrect.

    vv I got it now. Thanks for saving my hair.
    Last edited: Jan 25, 2006
  2. jcsd
  3. Jan 25, 2006 #2
    that's not the right equation; you should be using kinematics/rotational kinematics to find the time that it accelerates. The T in that equation is for period.
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