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Finding distance with a pivot

  1. Oct 18, 2007 #1
    1. The problem statement, all variables and given/known data

    The two objects in the figure below are balanced on the pivot, with m = 1.8 kg. What is the distance d?


    2. Relevant equations

    3. The attempt at a solution
    I haven't attempted a solution because I'm not sure how to set this problem up. I know that a Fnet must be found, and I know that the two masses would be in the equation and I know that the pivot would exert a normal force. I know part of the equation would be Fnet = N(pivot) - (m1 + m2)g, but where do the distances come into play?
  2. jcsd
  3. Oct 18, 2007 #2


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    Your approach will solve for the normal force at the pivot by setting Fnet=0 because the system is in translational equilibrium. But since the loads are balanced, you must also look at the rotational equilibrium about the pivot, wher the sum of the torques must be zero. Are you familiar with torque calculations for moments of the objects about the pivot point?
  4. Oct 18, 2007 #3
    No I'm not.
  5. Oct 18, 2007 #4


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    Torque of a mass about a point is just its weight times the perpendicular distance of its cg to the point. The torque of each mass must then balance. You'll have to draw a good sketch to get the proper distances involved.
  6. Oct 18, 2007 #5
    I have no idea how to do that.
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