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Homework Help: Angular velocity find angular displacement

  1. Jan 2, 2009 #1
    1. The problem statement, all variables and given/known data
    A body with moment of inertia 20kgm^2 is rotating about a fixed axis with an angular velocity of w(t)= 3t^2-4

    a. Through what angular displacement will the body move in the first 3 seconds
    b. What is the new torque exerted on the object at t=2

    2. Relevant equations
    Angular Kinematics equations

    3. The attempt at a solution

    I integrated the angular velocity to get the displacement to be Theta(t)=t^3-4t ... then I evaluated the definite integral from 0 to 3 to get 15. But 15 What? Am I doing this right?

    I don't know what to do for the second part. Does anyone know?
  2. jcsd
  3. Jan 2, 2009 #2
    b) What's angular acceleration and torque formula?
  4. Jan 2, 2009 #3
    torque = Ia so it would then be derivative of w(t)= 3t^2-4 to get 6t evaluated at 2 gets 12. Then you do 12 times 20 to get 240?
  5. Jan 2, 2009 #4
    Does any of this look good?
  6. Jan 3, 2009 #5
  7. Jan 3, 2009 #6


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    Homework Helper

    Looks good to me.
  8. Jan 3, 2009 #7


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    Science Advisor
    Homework Helper

    Hi tachu101! :smile:

    (have an omega: ω and a theta: θ :wink:)

    Yes, that's fine … and the 15 has no dimensions … it's just an angle (in degrees or radians, depending on what w is, so you needn't say).
    Also fine (though you could have stated it a little more logically :wink:)
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