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A Uniform Rod Is Attached To A Point With A String---Moments

  1. Aug 20, 2015 #1
    1. The problem statement, all variables and given/known data
    upload_2015-8-20_20-14-58.png

    Use the principle of moments and take moments about A to show that the weight of the object O is 19 N.


    2. Relevant equations

    Moment=Force x perpendicular distance
    3. The attempt at a solution
    Vertical component of tension= TsinA
    = 30sin50
    =23N
    (8.5 x 0.6) = (9.8M-23) x 1.2
    5.1/1.2 = 9.8M-23
    9.8M=27.25
    As w=mg, the W= 27.25N
    But the answer is supposed to be 19N
     
  2. jcsd
  3. Aug 20, 2015 #2
    You have made an error in balancing moments . Which moment acts in which direction ?
     
  4. Aug 20, 2015 #3
    One acts clockwise from point B, I am not so sure about the other. Does it act anticlockwise from point A or does it act at the centre?
     
  5. Aug 20, 2015 #4
    In which direction does gravity exert a force on M ? Is it in the direction of tension or the rod ?
     
  6. Aug 20, 2015 #5
    It exerts a force in the direction of the rod.
     
  7. Aug 20, 2015 #6
    So should it's moment add to that of the rod's , or should that of the tension's ?
     
  8. Aug 20, 2015 #7
    It should act to that of the rod.
     
  9. Aug 20, 2015 #8
    And what have you done in your original solution ?

    Hope this helps ,
    Qwertywerty .
     
  10. Aug 20, 2015 #9
    Thanks!
     
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