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Homework Help: Force exerted on a pivot point

  1. Oct 27, 2014 #1
    1. The problem statement, all variables and given/known data
    A horizontal plank 4.0 m long and having mass 24.0 kg rests on two pivot points, one left at the end and a second one 1.0 m from the right end. What is the magnitude of the force exerted on the plank by the second pivot point?

    2. Relevant equations

    3. The attempt at a solution
    I'm not even sure how to attempt this problem
  2. jcsd
  3. Oct 27, 2014 #2


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    Staff: Mentor

    Draw a large diagram and mark on the forces and their location.

    Take moments about a convenient point.
  4. Oct 28, 2014 #3
    Draw a free body diagram.
    Assuming the mass distribution is same, take the centre of mass at the centre i.e at 2.0 metre.
    The plank is in translational and rotational equilbrium.
    Thus, the sum of magnitude of the forces at the pivot is equal to the wieght of the plank.
    And, the moments, or the torque exerted by each of the pivot is equal and opposite thus their magnitudes are equal.
    Take the origin as the centre of mass.

    PS:- Torque= Force*distance of action from the origin (when force is perpendicular)
    In vector notation torque is the cross product of radius and force. But the above equation is enough here

    Hope it helps :)
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