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Homework Help: I Need Some Help Plz

  1. May 6, 2008 #1
    I Need Some Help Plz !!!

    Hi, I am needing some serious help on understanding the following question::frown:

    A uniform door (0.81 m wide and 2.1 m high) weighs 140 N and is hung on two hinges that fasten the long left side of the door to a vertical wall. The hinges are 2.1 m 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 (b ) the lower hinge. Determine the magnitude and direction of the force applied by the door to (c ) the upper hinge and (d ) the lower hinge.

    I have the answer in front of me from the answer book but I am having trouble understanding how they came to the final conclusion.


    Thank you very much!!
  2. jcsd
  3. May 6, 2008 #2

    Chi Meson

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    Science Advisor
    Homework Helper

    You must solve for balanced torques. Pick the lower hinge as a pivot point. The weight of the door acts as though it is a force that acts at the center of mass of the door.
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