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Uniform Rod?

  1. Feb 3, 2008 #1
    A uniform rod has length 87 m and mass 8 kg. A mass of 8 kg is attached at one end. The other end of the rod is pivoted about the horizontal axis.

    a) determine the torque immediately after the rod-plus-mass system is released from the horizontal position.

    b) After the rod-plus-mass system is released, it rotates freely. Determine its angular velocity as the rod passes through the vertical direction. Answer in units of s^-1

    c) The angle between the instantaneous position of the rod and the initial horizontal direction is 67 degrees. How much potential energy is released in going from 0 degrees to 67 degrees?
     
  2. jcsd
  3. Feb 3, 2008 #2
    I found how to do part a

    T = m(rod)gl +m(mass)gr
    T = 8(9.8)(87) + 8(9.8)(43.5)
    T = 10231.2 kgm^2/s^2

    still got no clue how to attack b or c.
     
  4. Feb 4, 2008 #3
    Found b...
    Στ=I*α

    I=8*87^2/3+8*87^2
    I=80736

    α=0.127 rad/s^2

    θ=π/2

    using energy
    m*g*h=.5*m*v^2=.5*I*ω^2

    9.81*(8*43.5+8*87)=.5*80736*ω^2
    0.50 rad/s

    P.S. Any help with c?
     
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