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Homework Help: Differentiation Help

  1. Aug 20, 2008 #1
    Differentiation Help!!

    1. The problem statement, all variables and given/known data
    A particle is moving along a straight line so that, at time t seconds after leaving a fixed point O, its velocity vms-1 is given by v=10sin(1/2 t).
    Find the time when the acceleration, given by dv/dt, is first zero.

    2. Relevant equations
    sinx differentiates to cosx

    3. The attempt at a solution
    Ok i know they are asking me to find the time where there is a stationary point so therefore the gradient or dv/dt = 0.
    From differentiating 10sin(1/2 t) i got 5cos(1/2 t). so therefore, 5cos(1/2 t)=0 so i thought you multiply by 2 to get rid of the half then divide by 10 so the Right hand side= 0 and then inverse cos of 0 = 1/2 Pi but the answer in the textbook gives Pi.
    Please help me any body!!
  2. jcsd
  3. Aug 20, 2008 #2


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    Homework Helper

    Re: Differentiation Help!!

    You've got the steps right, just note that it's 1/2t = arc cos 0 and not t = arc cos 0.
  4. Aug 20, 2008 #3
    Re: Differentiation Help!!

    ohhh yeah of course!! thank you very much =]
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