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Simillar long question which will come out during my test, need help

  1. Nov 23, 2013 #1
    1. The problem statement, all variables and given/known data

    Untitled_zps6644b296.png

    Untitled2_zps8609575f.png
    2. Relevant equations
    ƩMA = Ʃ r x F
    Total Force of x,y= 0
    root(rx^2+ry^2)= Magnitude
    3. The attempt at a solution

    I cannot find i)

    my method
    0=2000+3000(0.4)-Rc
    -3200N=-Rc(up)

    0=3200-2000-3000+Ry
    Rx=1800

    How to find to magnitude, when roller only got y force, i can't use root(rx^2+ry^2)
     
  2. jcsd
  3. Nov 24, 2013 #2

    haruspex

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    I've no idea how you get these equations, or what Rc stands for. Please explain your analysis.
    Since it's a roller against a vertical beam, I would think it can only provide an x force.
    But where's the difficulty in finding the magnitude if there were only a y force? What would root(0^2+ry^2) give you?
     
  4. Nov 24, 2013 #3
    They only provide 2 y force, so how i use that to find rx?
     
  5. Nov 24, 2013 #4
    You haven't shown us, or at least described in words, your free body diagram. Tell us what you got. That's key to the rest of the problem.
     
  6. Nov 24, 2013 #5
    My free body diagram got two reaction for at A, 1 reaction force at B at including the G2, G1 force and also one reaction force at C
     
  7. Nov 24, 2013 #6
    From the diagram, it doesn't seem that there is any reaction force at C. Next, please write for us your force balance in the vertical direction, your force balance in the horizontal direction, and your moment balance around around hinge A.
     
  8. Nov 25, 2013 #7
    3(0.7)+2(0)=Rb(0.8)=0
    Rb=2625


    I now know how to RX RY at hinge A and answer b, but c quite difficult. i need some guidance

    My guess is that I need to find the Rx Ry of the pulley and them derive the magintude of the F through Fr=root(x^2+y^2)
     
    Last edited: Nov 25, 2013
  9. Nov 25, 2013 #8
    You are missing the decimal point in your equation for Rb. To get Rx and Ry at A, you need to do horizontal and vertical force balances.

    Part c starts out with a geometry problem. You need to find out how far to the right point C is relative to point A, and you need to find out how far point C is above point A. Can you do the geometry to find out those distances?

    Chet
     
  10. Nov 26, 2013 #9
    Can check my working
    taking moment at A=2000cos35 (0.4) + 3000sin83.81(1.06) / 1.6(sin64.74) = (wrong answer)

    can anyone help me check

    AD= 1.6
    AG2=1.06
     
    Last edited: Nov 26, 2013
  11. Nov 26, 2013 #10
    I agree with your moment arm to G1, but, for the moment arm to G2, I get (0.8cos35+0.7sin35)=1.06

    Also, you left out the moments about A resulting from the horizontal and vertical components of rope tension at C.
     
  12. Nov 26, 2013 #11
    thanks
    Chestermiller i have solve the question.
    I appreciate your patient with me alot
     
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