Statics - Moments

  1. Last edited: Mar 2, 2009
  2. jcsd
  3. PhanthomJay

    PhanthomJay 6,186
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    Looks like you forgot to multiply by the moment arm perpendicular distance to the pivot. Also, check your signs for each of the torques.
     
  4. Yes, the distance x, correct ?? Its M= F . x .. But how can I find x ? :S
     
  5. PhanthomJay

    PhanthomJay 6,186
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    A torque of a force or force components is calculated by multiplying the force or force components times the perpendicular distance between the line of action of that force and the pivot. You alreadty I think have the vertical component of each force. So what's the perpendicular distance, and what are the signs of the torques?
     
  6. The first force is acting at a clockwise direction, it is positive.
    The second force is acting at an anti-clockwise direction, it is negative.

    Regarding the Perp. distance, its just not clicking in my head.
     
  7. Ok wait, do you mean by perp. distance is the distance given between the pivot and the force itself ?? Which is 3x10^-3 for F1 and 3.8x10^-3 for F2 ?
     
  8. PhanthomJay

    PhanthomJay 6,186
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    No, you are looking for the torque of both forces about the NUT. They both seem ccw, no? Also, regarding perpendicular distance from the horizontal force components to the nut, they are ___ and ___ for each horizontal force component?
     
  9. Ok I think i got it :D :D

    http://img80.imageshack.us/img80/2008/image167k.jpg

    Im not sure about the final result though, is it N or Kn or Nm ..
    The given answer is 81.1N .. I found 8116 .. hmm if the supposed answer is 81.1Kn then my answer would be correct for N.

    Correct me if im mistaken.
     
    Last edited: Mar 2, 2009
  10. PhanthomJay

    PhanthomJay 6,186
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    Watch your units. If the torque is in N.m, then Force should be in Newtons and distance should be expressed in meters.
     
  11. So where does that leave me ?? Am I supposed to convert or anything ?? If I divide by 100 I get the correct answer. But I want to know why am I dividing by a hundred.

    Can you please tell me ? I got test tomorrow and its getting late =\
    I really need to know how to correct my mistakes !
     
  12. Bump =\
     
  13. PhanthomJay

    PhanthomJay 6,186
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    It must be your algebra:
    Fsin60(.3m) + Fsin70(.38m) = 50N.m
    F= 80.1N
     
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