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Statics question: calculate forces and reactions in tow-truck problem

  1. Nov 22, 2009 #1
    1. The problem statement, all variables and given/known data

    "A lifting mechanism is mounted on the back of a truck as shown: Calculate the forces in each member and the reactions @ A & B for alpha=0


    2. Relevant equations

    Sum of moments about A=0:
    0=(5000N)(1m)+(-5000N)(-1.25m)+(By)(.5m)
    By=2500N

    3. The attempt at a solution

    I treated the entire assembly as a rigid body to get the force By above; that would make Ay=2500N, correct?

    I have drawn the entire FDB in AutoCAD, and have found the following:

    BD=6250N
    CD=3750N
    AB=2500N
    AC=5590.167N
    BC=5000N

    I have attached a scan of the problem. Now, having said all of that, is my general thinking ok? We're supposed to be able to figure out the reactions @ A and B using the method of joints, but I'm having real trouble with that. I found the reactions by using moments around A and then summing my forces in the Y direction=0, and got my forces in the members by using trig, but I also need to figure out which members are in tension/compression, again, using method of joints. If someone could step me through finding the forces at any two joints, I think that in itself would be a very helpful start! Thanks in advance for any/all helpful replies
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
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