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Force systems, couples

  1. Jan 26, 2013 #1
    1. The problem statement, all variables and given/known data
    A force F of magnitude 50 N is exerted on the automobile parking-brake lever at the position x=250 mm. Replace the force by an equivalent force-couple system at the pivot point O.

    Picture: http://i.imgur.com/dJGtvAo.png


    2. Relevant equations

    M=F*d
    3. The attempt at a solution

    I have replaced the force by an equivalent force-system at O so I now the exact same force F(both magnitude and direction) but at O. Now I want to find the moment which is given by M=Force*distance. The distance I need is the closest distance between O and the "moment-point". For simplicity I instead try to find the distance between O and Fcos20. But I have problems finding it.
     
  2. jcsd
  3. Jan 26, 2013 #2

    tiny-tim

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    hi zeralda21! :smile:
    no, it's the closest distance between O and the line of the force

    probably easiest to start by extending the left-hand part until it reaches the line of F, and finding the total length of that :wink:
     
  4. Jan 26, 2013 #3
    Ouch, that is actually what i meant. But the closest distance is therefore the horizontal distance from O to Fcos(20), no? I'm not sure what you mean. Extend it as:

    0.1m+xcot15 ?
     
  5. Jan 26, 2013 #4

    tiny-tim

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    hi zeralda21! :wink:
    on second thoughts, i don't think that works :redface:

    try it this way …

    draw a line OG parallel to the line of F

    then the distance is the sum of the perpendicular distances from that dot in the middle to the line of F, and from that dot in the middle to OG :smile:
     
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