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Need assistance in Physics question relevant to Torque & Static equlibrium

  1. Nov 9, 2014 #1
    1. The problem statement, all variables and given/known data
    tens.png

    2. Relevant equations
    Static equilibrium: Net force & net torque = 0

    3. The attempt at a solution
    attempt.jpg


    Am i doing this correctly for part a?
     
  2. jcsd
  3. Nov 9, 2014 #2
    Are we to assume that there are no forces on the bolts?
     
  4. Nov 9, 2014 #3

    SteamKing

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    You are introducing an extra quantity d1 into your calculations, which will be difficult to calculate. Find an expression for sin θ based on L and H for the gantry crane as shown in the diagram.
     
  5. Nov 9, 2014 #4
    Either way even with replacing d1 with H, I still get Ft = (mgx+MgL/2) /(L sin(theta) ) . Am I on the right step?
     
  6. Nov 9, 2014 #5

    SteamKing

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    d1 ≠ H, and the expression for sin θ is a little more complicated than that. Your expression for FT is correct.
     
  7. Nov 9, 2014 #6
    If I can't call the line of the pivot point perpendicular to the cable d1, what should I call it? I'm a little confused on what you mean. Isn't that all I'm looking for anyways: the tension in the cable as a function of the load position x? - which was the expression i found?. :/
     
  8. Nov 9, 2014 #7
    Yes, it's absolutely fine. But can you express sin theta in terms of H and L ?
     
  9. Nov 9, 2014 #8
    Yes you would get sin(theta) = H/L ----> H=Lsin(theta). So then my final answer would be Ft = (mgx+MgL/2) /(L sin(theta) ) ----> Ft = (mgx+MgL/2) /(H). Much better I hope? :]
     
  10. Nov 9, 2014 #9

    SteamKing

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    There's another triangle (which you are overlooking) which can give you an expression for sin θ. (Hint: the cable holding the support arm forms the hypotenuse of this triangle)
     
  11. Nov 9, 2014 #10
    Nope. Try again.
     
  12. Nov 9, 2014 #11
    The only triangle I see is the top triangle and bottom triangle and the triangle on the left with d1.

    sin theta = H/L

    How else can you derive the sin theta?
     
  13. Nov 9, 2014 #12

    SteamKing

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    sin θ is not H / L. You should review your trigonometry, especially the definitions of the sine, the cosine, and the tangent.
     
  14. Nov 10, 2014 #13
    Sorry about that, sin theta = H / sqrt (L^2 + H^2) :D
     
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