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posted by  nightstar918 on 11/7/2009 12:56:09 AM  |  status: Live  |  Earned Karma: 35

Rotation, Torque, angular acceleration

Course Textbook Chapter Problem Needs by
Calculus Based Physics Fundamentals of Physics Extended (8th) by Halliday, Resnick, Walker 10 74 11/7/2009 at 11:00:00 PM
Question Details:
Attached to each end of a thin steel rod of length 1.20 m and mass 6.40 kg is a small ball of mass 1.06 kg. The rod is constrained to rotate in a horizontal plane about a vertical axis through its midpoint. At a certain instant, it is rotating at 39.0 rev/s. Because of friction, it slows to a stop in 32.0 s. Assuming a constant retarding torque due to friction, compute (a) the angular acceleration, (b) the retarding torque, (c) the total energy transferred from mechanical energy to thermal energy by friction, and (d) the number of revolutions rotated during the 32.0 s.
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posted by Kevin_08 on 11/7/2009 1:01:18 AM  |  status: Live
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Response Details:
Given that
 intial angular acceleration ω0
 final angular accleration ω = which is constant
 α = angular accleration
 by using kinematic eq = 0 = ω0 +αt
                                        = α = -ω0/t
                                              = - 39/32 = - 1.21 rev/s
                                    α = -1.21 *2π = - 7.66 rad/s2
 (B) the moment of inertia of rod = I = Ml2/12
the contribution of each ball = M(l/2)2
 total moment of inertia  = I = Ml2/12 + 2 ml2/4
        plug values and                                    do caliculations for I
 (c) since the system comes to rest the mechnical energy is converted to thermal energy which is simply intial kinetic energy
      Ki = 1/2 Iω02
  plug values docaliculations for Ki----J
(d) applying kinematic eq =
            θ = ω0t + 1/2 αt2
                2π ( 39) (32) +1/2 (-7.66) (32)2
        docaliculations and that value gives angular displacement
(e) only mechnial energy is converted into thermal energy can still be computed without any additional information
I hope this helps! Best of luck with the rest of your coursework.
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