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Homework Help: Angular Velocity and Acceleration - Stumped!

  1. Aug 25, 2012 #1
    Hi guys,

    I'm stumped on just one question and not sure where to go with it now. Any help would be greatly appreciated...

    Calculate the angular acceleration and angular velocity of a 2kg object rotating in a circle of 1.5m radius in a time of 3s.

    My first answer i realise now was wrong due to calculating linear velocity

    Second answer:

    ω=3*(2∏)2=6∏ rad/s

    ∴ α=ω2r=(6∏)2*1.5=532.96 rad/s2

    Can anyone offer some assistance on where i'm going wrong here please?
  2. jcsd
  3. Aug 25, 2012 #2
    The acceleration you are calculating is centripetal acceleration . :O
  4. Aug 25, 2012 #3
    To compute the angular velocity, all you need is the period of on rotation. It does not depend on the radius, nor does it depend on the mass.

    To compute the angular acceleration, you need to know how angular velocity changes. The problem has no data on this.
  5. Aug 25, 2012 #4


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    welcome to pf!

    hi bruvvers! welcome to pf! :smile:

    hmm … you're obviously completely confused about the difference between angular and linear measurements, and between angular acceleration and centripetal acceleration

    ω2r (= v2/r) is the formula for centripetal acceleration

    centripetal acceleration is simply the component of linear acceleration in the (negative) radial direction

    centripetal acceleration is measured in m/s2

    centripetal acceleration has nothing to do with angular acceleration!

    angular acceleration is measured in rad/s2
    i'm not sure what you've done here :confused:

    (and your arithmetic isn't correct anyway :redface:)

    the question is …
    … does this mean that it is rotating at a constant angular speed? if so, the angular acceleration is obviously zero! :rolleyes:

    … or does it mean that it starts from rest, accelerates uniformly, and completes its first circle in 3s ? if so, use the standard constant acceleration formulas, adapted for constant angular acceleration

    show us what you get :smile:
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