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Drawing free body diagrams (torque; rotational motion)

  1. Mar 16, 2017 #1
    1. The problem statement, all variables and given/known data
    A 500-N person stands 2.5 m from a wall against which a horizontal beam is attached. The beam is 6 m long and weighs 200N (see diagram below). A cable attached to the free end of the beam makes an angle of 45 degrees to the horizontal and is attached to the wall.
    ph1.jpg ph2.jpg
    2. Relevant equations
    I'm not sure what is the force R mean in the answer, and why is it pointing in an angle theta instead of perpendicular to the wall.

    3. The attempt at a solution
    I drew a normal force at the end of the beam perpendicular to the wall, which is apparently not the right answer haha.
     
  2. jcsd
  3. Mar 16, 2017 #2

    ehild

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    Hi Janet, welcome to Physics Forums!
    The beam is attached to the wall by a pivot, and the pivot can act with force at an angle.

    upload_2017-3-17_5-3-7.png
     
  4. Mar 17, 2017 #3

    CWatters

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    +1

    Its not hard to see why that force must have a vertical component - if it didn't the beam would fall down.
     
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