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Mechanic Equilibrium problem

  1. Mar 26, 2012 #1
    Mass of man is = 80KG
    Mass of the ladder is = 20 KG

    Mass of the bar connecting the two halves of the ladder is negligible.

    The friction force between floor and ladders are negligible. (floor is frictionless)

    Question: find the tension in the horizontal bar connecting
    the two halves of the ladder...


    Here is the figure:
    ex30.png





    I am wondering if it is possible to calculate the tension, without knowing the dimensions of the ladder??It is not right?
     
  2. jcsd
  3. Mar 26, 2012 #2

    ehild

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    The figure is very impressive! :smile:

    It is possible. Write up the equation for the momenta.


    ehild
     
  4. Mar 26, 2012 #3
    Equations for momenta, i think you mean torque right?.
     
  5. Mar 26, 2012 #4

    ehild

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    Yes, of course, sorry. I talked about torque in my language just before writing this letter and mixed.

    Measure lengths in the unit shown in the figure when writing up the torques. But you need the angle between the legs of the ladder. It must be given.


    ehild
     
    Last edited: Mar 26, 2012
  6. Mar 26, 2012 #5
    First of all i need to do a diagram of forces.

    Is that right?
    ex30.jpg


    Ok so without the angle is is impossible to do the exercise?
     
    Last edited: Mar 26, 2012
  7. Mar 26, 2012 #6

    ehild

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    It looks all right if the distances are correct.



    ehild
     
  8. Mar 26, 2012 #7

    ehild

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    Hi Fabio,

    Can you proceed?
    Write up the equations for the y components of forces for both legs, and also the torques. For those, you need the angle. Adding up the equations for the force components, you get N1+N2. Subtracting the equations for the torques, you get N1-N2. Determine them and use in the torque equation for one leg.


    I go to sleep:zzz:

    ehild
     
  9. Mar 29, 2012 #8
    I talked to my teacher and he said that the exercise should have the dimensions.
    And with the dimensions i could calculate the angle and do the exercise.

    I have it done. Thanks for your help :)
     
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