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Homework Help: Torque- rigid objects in equalibrium/ center of gravity. need help

  1. Dec 22, 2011 #1
    1. The problem statement, all variables and given/known data
    A uniform door(.81m wide and 2.1m high) weighs 140N and is hung on two hinges that fasten the long left side of the door to a vertical wall. The hinges are 2.1m apart. Assume that the lower hinge bears all the weight of the door. Find the magnitude and direction of the horizontal component of the force applied to the door by a) the upper hinge and the lower hinge. Determine the magnitude and direction of the force applied by the door to b) the upper hinge and the lower hinge.

    Fg = 140 N

    2. Relevant equations
    ƩT = F L
    am stuck on how the torque equation applies to this problem

    3. The attempt at a solution
    i drew the diagram of the door and the hinges spaced 2.01 m apart.
    I think you have to make the pivot point/axle point at the bottom hinge

    sum of the verticle forces = weight of the door, im assuming this.
    Am not sure how to even begin this question. but do i start to make x components at the hinges?

    any advice would be helpfull.

  2. jcsd
  3. Dec 22, 2011 #2


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    Staff Emeritus
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    Hello utnip. Welcome to PF !

    Assume that gravity acts downward on the door at its center. That will produce a torque about the hinges. Find the torque about the lower hinge.
  4. Dec 23, 2011 #3
    See image below

    Attached Files:

  5. Jul 27, 2012 #4
    but where is your axis on the door?
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