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Homework Help: Physics Problem Involving Moment and Acceleration

  1. Nov 18, 2013 #1
    A uniform board length L hinged about its lower end, held at θ above the horizontal is released from rest. As it passes through the horizontal what is the tangential acceleration of its outer tip?

    At first when I attempted this, I applied conservation of energy.
    (1/2)mv^2+mgh=(1/2)mv^2 + mgh
    but I did not get an answer.
    Then I decided could the answer just be L*gravity?? Any help given will be much apreciated! Thank you!
  2. jcsd
  3. Nov 18, 2013 #2


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    Science Advisor
    Homework Helper

    welcome to pf!

    hi taylorkrauss! welcome to pf! :smile:

    your kinetic energy must include the rotational KE:

    KE = 1/2 mvc.o.m2 + 1/2 Ic.o.mω2 = 1/2 Ic.o.rω2 :wink:
  4. Nov 18, 2013 #3


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    Staff: Mentor

    You're looking for tangential acceleration, not velocity. So think about the moment of inertia, where the center of rotation is, and what forces are acting to produce a torque at the instant in question.
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