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Angular revolution deceleration

  1. Apr 19, 2009 #1
    http://img15.imageshack.us/img15/858/masteringf.jpg [Broken]

    a:
    550-150 = 400rev change
    400/60 = 6&2/3 rev/s (converted to revs)
    6.66666 / 3.5 seconds = 1.9 rads^-2

    since it's decelerating i put -1.9 rads^-2






    now part two i got wrong,
    b:
    [tex]\theta[/tex]f=[tex]\theta[/tex]i + [tex]\omega[/tex]i * t + 1/2 [tex]\alpha[/tex] t^2

    so i got the angle it turns through in radians being

    wi * t + 1/2at^2

    wi = 550*2[tex]\pi[/tex][tex]\underbrace{}_{}[/tex]t

    wi = 57.59 rad/s (please check this i think this may be where i went wrong)


    so radian angle = 57.59 *3.5 + (1/2*(-1.9) ) *3.5^2

    i got 189 radians

    189 / 2[tex]\pi[/tex] = 30 revolutions

    and i got it wrong





    c: part three of the question:

    wf = wi + at

    0 = wf (from question) + at

    wf = (150 *2[tex]\pi[/tex])/60 = 15.7 rad/s

    0 = 15.7 + (-1.9 *t)
    -15.7/-1.9 = t
    t=8.26 seconds

    and i got it wrong
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 19, 2009 #2
    anyone?
     
  4. Apr 19, 2009 #3

    Doc Al

    User Avatar

    Staff: Mentor

    This acceleration is in rev/sec^2, not rad/sec^2.

    (This affects parts B and C.)
     
  5. Apr 20, 2009 #4
    it was in rev/sec^2

    i figured it out, i had used rev/min instead of rev/s with [tex]omega[/tex]i
    i.e i used 400 rev/s^2 thanks for the help
     
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