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Calculating Average Angular Velocity

  1. Oct 28, 2012 #1
    1. The problem statement, all variables and given/known data
    At t=0 the current to a dc electric motor is reversed, resulting in an angular displacement of the motor shaft given by
    theta(t)=246t-20.6t^2-1.47t^3

    Calculate the average angular velocity for the time period from t=0 to the time calculated when the angular velocity of the motor shaft is 0.

    2. Relevant equations
    delta(omega)/delta(time)


    3. The attempt at a solution
    The time the velocity of the motor shaft is 4.14. I got that from taking the derivative and solving for t=0.
    I'm confused as to why my answer is wrong, when I plug in 4.14 into
    246-41.2t-4.41t^2 to calculate the average angular velocity I get.
    (2(41.2)(4.14)-4.41(4.14)^2-246)/(4.14-0)
    I get an answer of -59.46 rad/s.

    Can't seem to find where I went wrong, I did this on paper as well as on calculator to make sure I wasn't punching it in wrong and I came out with approximately the same result.
     
  2. jcsd
  3. Oct 28, 2012 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Note that the question asks for average angular velocity (not instantaneous velocity).
     
  4. Oct 28, 2012 #3
    Ah... thank you, I was helping someone with this and just couldn't seem to find my error.
     
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