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Homework Help: Rotational kinematics help

  1. Oct 22, 2012 #1
    A flywheel 1.2 m in diameter is uniformly accelerated from rest and revolves completely 68 times in reaching a speed of 125 rev/min. Find the time taken to reach this speed

    i have been given the correct answer as 65.29 seconds

    Wht i have up to now

    ω1 = 0
    ω2 = 125 r/min = 125/60 = 2.083 r/s
    theta = 68*2∏ = 427.26 rads
    t = ?

    I have tried to use theta = ((ω1+ω2)*t)/2 rearranged to get t = 2theta/ω1+ω2 however my answer doesnt come close

    Any suggestions would be appreciated
  2. jcsd
  3. Oct 22, 2012 #2
    you need the equation of motion for rotation. the flywheel is undergoing uniform acceleration; you need to take that into consideration.
  4. Oct 22, 2012 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Make sure ω is in rads/sec.
  5. Oct 22, 2012 #4
    That sorted it, silly mistake, Thanks Doc Al
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