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Homework Help: Rotating Disk Question

  1. Oct 28, 2007 #1
    1. The problem statement, all variables and given/known data
    A disk rotates about its central axis starting from rest and accelerates with constant angular acceleration. At one time it is rotating at 7.0 rev/s; 83 revolutions later, its angular speed is 18 rev/s. Calculate (a) the angular acceleration (rev/s^2), (b) the time required to complete the 83 revolutions, (c) the time required to reach the 7.0 rev/s angular speed, and (d) the number of revolutions from rest until the time the disk reaches the 7.0 rev/s angular speed.

    2. Relevant equations
    (a) ang accl=(W2^2-W1^2)/2(change in theta)
    (d) change in theta= W0t + 1/2 ang accl t^2

    3. The attempt at a solution
    I got the answers to both (b) and (c) but my (a) was not correct and it's weird because I used my answer from (a) to do both (b) and (c), my answer to (a) was 10.408 rad/s^2 and calculated by plugging in 36pi as W2, 14pi for W1 and change in theta as 166pi... What am I doing wrong here??

    Also, for part (d) I was told to use to the time I recieved from part (c) to find the change in theta and I got 150 rev, and that's obviously wrong... what am I doing wrong with this one as well??
  2. jcsd
  3. Oct 28, 2007 #2
    The problem asks for the angular acceleration in rev/s^2, you found the angular acceleration in radians/s^2, just convert the units.
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