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Magnitude at pivot point and A

  1. Mar 27, 2014 #1
    So this is the question that is given

    The right-angle uniform slender bar AOB has mass m. If friction at the pivot O is neglected,
    determine the magnitude of the normal force at A and the magnitude of the pin reaction at O.

    Now I don't really know where to start whit this or what to do at all. Any help with this would me greatly appreciated

    Thanks
    Joey
     

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  2. jcsd
  3. Mar 27, 2014 #2

    SteamKing

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    Start by drawing a free body diagram. It would appear that both arms of the L would have the same mass per unit length, so you can use this assumption to find the weight of each arm in order to calculate the reactions at A and O. Once you have your FBD constructed, then you can write equations of static equilibrium.
     
  4. Mar 27, 2014 #3
    Thanks for the quick response. I have thought of that but how do I go about finding the masses without any information besides that AO = 2l/3, OB=l/2 and that 30o degree angle at A.

    With the free body diagram, Ill have downwards force(gravity), a force pushing back on A, anti-clockwise force at A and the clockwise force at B right?

    This parts of mechanics is just beating me at this stage

    Cheers
    Joey
     
  5. Mar 28, 2014 #4

    SteamKing

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    Like I suggested in my reply, assume a constant mass per unit length, ρ, and develop the mass of the two arms. Your final reactions will be expressions containing ρ, unless it cancels out somewhere along the line.
     
  6. Mar 28, 2014 #5
    Does this mean that AO will have a mass of (2l/3)(p) and OB will have a mass of (l/2)(p)?
     
  7. Mar 28, 2014 #6

    SteamKing

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  8. Mar 28, 2014 #7
    So ill add both of these together to get the complete mass of the object, Should i then treat it as AO and then OB or do you wrok with the whole object i.e can it be two separate ladders leaning against a point or not?
     
  9. Mar 29, 2014 #8

    SteamKing

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    AOB is a single bar in the shape of a lazy L, not a couple of ladders.
     
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