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Homework Help: Acceleration at constant velocity?

  1. May 25, 2014 #1
    1. The problem statement, all variables and given/known data

    Calculate the torque, t about origin that must be applied to a particle for it to maintain a constant speed v along a cardiod.

    2. Relevant equations

    t = r x f

    a = (r_dot dot - r*Θ_dot ^2) r_hat + (r*Θ_dot dot + 2 r_dot * theta_dot) theta_hat

    3. The attempt at a solution

    Constant speed means that the derivative of the speed wrt time = 0 = magnitude of the acceleration. But then if the mag of the accleration is zero then everything turns to zero because it is all related. So I'm guess there is something else which constant speed implies and I am wrong. What is it?
  2. jcsd
  3. May 25, 2014 #2
    Velocity is a vector quantity, so, if the direction of the velocity vector changes, that constitutes acceleration also. It's not only the speed that counts, it's also the direction.

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