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Constant angular acceleration problem

  1. Nov 4, 2007 #1
    A)If it took 0.480 s for the drive to make its second complete revolution, how long did it take to make the first complete revolution?

    B)What is its angular acceleration, in rad/s^2?

    please help
     
  2. jcsd
  3. Nov 4, 2007 #2

    G01

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    OK, in order for to give you some help, I am going to need to things. I need to see some of your work, following the rules of the forum, and I'll need the whole question. It doesn't seem like you supplied enough information here.

    If you don't have any calculations to show yet, at least point out the formulas and concepts that you think apply, etc. You must know something about the problem.
     
  4. Nov 4, 2007 #3
    does this Equation work?
    deta-deta.not = (1/2)(w2+w1)t in order to find t

    since we know total angle
     
  5. Nov 4, 2007 #4

    G01

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    What is deta-deta.not, and what is the full question??
     
  6. Nov 4, 2007 #5
    (anglefinal - anglebeginning) = (1/2)(omega2+omega1)*t
     
  7. Nov 4, 2007 #6

    G01

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    That is a correct formula, but again, I can't tell you if it will be useful or not if you don't give me the whole question. It seems obvious that there is more to the problem. In part A, you make reference to "the" drive, thus assuming it has been mentioned before, and as far as I can tell, there is not enough information given in what you posted to solve the problem.
     
  8. Nov 4, 2007 #7
    The computer disk drive is turned on starting from rest and has constant angular acceleration.

    A)If it took 0.480 s for the drive to make its second complete revolution, how long did it take to make the first complete revolution?

    that all it say in the book :(
     
  9. Nov 4, 2007 #8

    G01

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    AHH ok! The drive starts spinning at rest. The formula you supplied last time should work, but I think you may want to consider using another (see hint).

    HINT: Finding the acceleration first, from the information from the first rotation may be beneficial. Can you give me an equation relating the angular acceleration to the speed, angular displacement and time of the first rotation? You should then be able to use that acceleration to help you find the answer to part A.
     
  10. Nov 4, 2007 #9
    i'm not sure but

    omega2=omega1+a*t

    or

    omega2^2=omega1^2 + 2*a*(angle2-angle1)
     
  11. Nov 5, 2007 #10

    G01

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    Yes, you can use both of those to find the angular acceleration.

    Can you find it now using one of these formulas and the information about the first rotation?
     
  12. Nov 5, 2007 #11
    what is t in that equation??? time after 2nd revolution or 1st revolution. also how can i solve it when it did not give the angular acceleration???
     
  13. Nov 5, 2007 #12
    (anglefinal - anglebeginning) = omega1*t+(1/2)a*t^2

    t=0.480 s

    4pi = 1/2*a*(0.480)^2

    8pi/(0.480)^2 = a

    a= 109.083 rad/s^2

    still give me wrong answer for angular acceleration :(
     
  14. Nov 5, 2007 #13
    can someone help me please . seem like GO1 offline -_-'
     
  15. Nov 5, 2007 #14
    whered da 4pi come from???
     
  16. Nov 5, 2007 #15
    can someone tell me why it give me wrong answer for angular acceleration?
     
  17. Nov 5, 2007 #16
    it should be......

    -4pi*t = 1/2*a*(0.480)^2....

    now tell me wats ur time after one revolution????and how did u get it???
     
  18. Nov 5, 2007 #17
    i need to find a first than find time after that
     
  19. Nov 5, 2007 #18
    ignore da above comment...........it should be......

    -(2/.480)2pi*t = 1/2*a*(0.480)^2....

    now tell me wats ur time after one revolution????and how did u get it???
     
  20. Nov 5, 2007 #19
    (anglefinal - anglebeginning) = omega1*t+(1/2)a*t^2

    omega1 = 0 because it start from rest

    4pi = 2 rev
     
  21. Nov 5, 2007 #20
    what equation u using ?
     
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