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Rotation Question

  1. Oct 24, 2007 #1
    A merry-go-round rotates from rest with an angular acceleration of 1.65 rad/s2. How long does it take to rotate through (a) the first 2.53 rev and (b) the next 2.53 rev?

    2. Relevant equations

    3. The attempt at a solution
    I tried to do this and I converted the rev to radians by multiplying the revolutions by 2pi and then for (a) I divided 15.896/1.65 and got 6.28 seconds (15.896 is 2.53(2pi))and for (b) I divided 31.79/1.65 to get 19.3 seconds. What am I doing wrong here?
  2. jcsd
  3. Oct 24, 2007 #2


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    Check your units, this doesn't work out to seconds.

    What equation relates time, angular displacement, and angular acceleration?
  4. Oct 24, 2007 #3
    theta-theta initial= w initial(t) + (1/2)at^2?
  5. Oct 24, 2007 #4


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    What do you get for the time with that equation?
  6. Oct 25, 2007 #5
    For (a) I got 1.75seconds and for (b) I got 2.48 seconds. I used 2.53 as the first displacement and for w I put in 0 and for acceleration I put 1.65 and then solved for t and that's what I got, and for the second part I put in 5.06 for the displacement. What am I doing wrong?
  7. Oct 25, 2007 #6


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    You need to change this into radians before using it in your calculations. Your units are not consistent otherwise. Try part (a) again with that change.

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