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A rope of 5m is fastened to two hooks 4m apart on a horizontal ceiling

  1. Oct 29, 2011 #1
    1. The problem statement, all variables and given/known data
    A rope of 5m is fastened to two hooks 4m apart on a horizontal ceiling. To the rope is attached 10kg mass so that the segment of the rope are 3m and 2m.Compute the tension in the string


    2. Relevant equations

    Sine rule

    3. The attempt at a solution
    I get stuck at the part that says '10kg mass so that the segment of the rope are 3m and 2m'. Please i just need the right diagram i know what to do.
     
  2. jcsd
  3. Oct 29, 2011 #2
    Re: Equilibrium

    Let us imagine we are hanging the mass to the rope.Right?
     
  4. Oct 29, 2011 #3
    Re: Equilibrium

    Yes.
     
  5. Oct 29, 2011 #4
    Re: Equilibrium

    So if one fastened a 5m rope to two hooks at a horizontal distance 4m apart, the rope will hang in a curve. But when the mass is hung at the specified point, what will happen to the rope? (assume the rope does not extend)
     
  6. Oct 29, 2011 #5
    Re: Equilibrium

    We are trying to do it together!
     
  7. Oct 29, 2011 #6
    Re: Equilibrium

    A triangle is formed.
     
  8. Oct 29, 2011 #7
    Re: Equilibrium

    So one knows the all the sides of this triangle. But I do not think that he sine rule can be used because there are to many unknowns for this rule to be used. Hence one can use the cosine rule to find the angles.
     
  9. Oct 29, 2011 #8
    Re: Equilibrium

    Ok lemme try it out.
     
    Last edited: Oct 29, 2011
  10. Oct 29, 2011 #9
    Re: Equilibrium

    I got the angles to be 104,47 and 29 am i right and what next?
     
  11. Oct 30, 2011 #10
    Re: Equilibrium

    Correct but it is better to work with 104.5, 46.6 and 29.0 deg.

    Now you can either use the sine rule or use components of the tensions.
     
  12. Oct 30, 2011 #11
    Re: Equilibrium

    Here is a diagram.
     

    Attached Files:

  13. Oct 30, 2011 #12
    Re: Equilibrium

    i got the tension to be 73.5N and 49.1N
     
    Last edited: Oct 30, 2011
  14. Oct 30, 2011 #13
    Re: Equilibrium

    if you show the working I can tell you where there is something not correct.
     
  15. Oct 30, 2011 #14
    Re: Equilibrium

    Here it is.
     

    Attached Files:

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  16. Oct 30, 2011 #15
    Re: Equilibrium

    Using the sine rule is ok but it is being used in the wrong triangle. Note that the tiangle of the set up of the apparatus is not necessarily a traingle of forces. In fact the triangle you are using is a traingle of distances not forces.

    Try to draw a triagle of the forces showing the directions of the weight, tension1 and tension2. Then put the angles required for this traingle of forces. If you need further help just ask.
     
  17. Oct 30, 2011 #16
    Re: Equilibrium

    Need help don't know what to do.:confused:
     
  18. Oct 30, 2011 #17
    Re: Equilibrium

    Look at the diagram of the forces and fit in its angles using information form the diagram of the apparatus.
     

    Attached Files:

  19. Oct 30, 2011 #18
    Re: Equilibrium

    Ok is this it?
     

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  20. Oct 30, 2011 #19
    Re: Equilibrium

    How can the angle at the bottom of your diagram be 104deg if it must be LESS than 90deg.
    Try again to get the angles of the FORCES diagram. The information required for this can be obained from the diagram of the strings attached to the mass.
     
  21. Oct 30, 2011 #20
    Re: Equilibrium

    For example tension T1 will make angle 43.4deg with the vertical.
     
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