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Three people are balanced on a uniform seesaw - Torque

  1. Apr 27, 2013 #1
    Three people are balanced on a uniform seesaw -- Torque

    1. The problem statement, all variables and given/known data
    Three people are balanced on a uniform seesaw which has a weight of 150 N as shown in the figure.
    Find the mass of person B and the normal force acting on the fulcrum.


    2. Relevant equations
    Tcw=Tccw


    3. The attempt at a solution
    There was a problem that involved mass and a fulcrum in my notes, it doesn't have a force or weight of the fulcrum, but I tried to set it up like the example to find the mass of person B

    (mC)(5.4)=(mA)(0)+(mB)(1.2). I then solved for mass B. I am not sure if I have to also put the weight of the fulcrum in there or not.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Apr 27, 2013 #2

    mfb

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    2016 Award

    Staff: Mentor

    There is no mass of a fulcrum. The 150 N refer to the weight of the horizontal seesaw. You can just treat it like an additional person, sitting at the center of mass of the seesaw. The sketch shows this.
    Those are not the distances to the fulcrum.
     
  4. Apr 27, 2013 #3
    So would I change the distances by subtracting the number from the fulcrum. Instead of mB being 1.2, it would be 0.8, mC 3.4 and mA 2?
     
  5. Apr 27, 2013 #4

    mfb

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    2016 Award

    Staff: Mentor

    Right. And don't forget the weight of the seesaw.
     
  6. Apr 27, 2013 #5
    Cool. Thanks!
     
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