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Angular Acceleration of a falling pole

  1. Nov 11, 2009 #1
    1. The problem statement, all variables and given/known data

    A 7.0m -tall electrical pole with mass 260 kg has a 42 kg electrical transformer attached to its very top. The pole is hit by lightning at its base, nearly severing the pole from its base. The pole begins to fall, rotating about the part still connected to the base.

    Estimate the pole's angular acceleration when it has fallen by 25 degrees from the vertical.

    2. Relevant equations

    Angular Acceleration = Net torque / Inertia
    Torque = r*perpendicular force
    Inertia = m1*r1^2+m2*r2^2*m3*r3^3 etc

    3. The attempt at a solution

    So I started out working on the Torque
    T1=7*42*-9.8*sin(25)
    T2= 3.5*9.8*260*sin(25)

    This gave me
    T1=381.3
    T2 = 1180.3

    Thus net torque = 381.3+1180.3 = 1561.6

    Then I started on the inertia:
    I = 42*7^2+(1/3)*260*7^2
    I = 6304.666

    So the acceleration is 1561.6/6304.666
    A= 0.247 rads/s^2

    This answer isn't right, but I can't figure out how I went wrong.
    Any help would be greatly appreciated.
     
  2. jcsd
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