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Need help with a seesaw torque question.

  1. Jan 11, 2012 #1
    1. The problem statement, all variables and given/known data
    Halle and Susan, each of mass 40 kg are sitting at opposite ends of a playground seesaw. The seesaw is stationary in the horizontal position and is 4.50 m long. Susan decides to jump off. Calculate the size of the unbalanced torque that now acts on the seesaw.


    2. Relevant equations
    torque= F * r (perpendicular distance?)
    F=ma


    3. The attempt at a solution
    I'm not sure how to find the perpendicular distance from the line of action of the force to the axis of rotation. I think F would be 40*9.8=392 N but I don't know how to find the "r" value.
     
  2. jcsd
  3. Jan 11, 2012 #2

    Doc Al

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    Staff: Mentor

    How far is she from the pivot of the seesaw? (You're given the full length of the seesaw.)
     
  4. Jan 11, 2012 #3
    It doesn't state the value in the question so I guess you are supposed to assume that she is half way. So 4.5/2=2.25 m
     
  5. Jan 11, 2012 #4

    Doc Al

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    Staff: Mentor

    Yes, that's what I would assume. The axis of the seesaw is in the middle and she is sitting at one end.
     
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