1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Statics - 3 Dimensional Equilibrium

  1. Jun 14, 2010 #1
    Moment about an axis - Statics - 3 Dimensional Equilibrium

    1. The problem statement, all variables and given/known data
    The member is supported by a pin at A and a cable BC. If the load at D is 300, determine the x, y, z components of reaction at these supports.
    i.e Find the reactions at A and the tension in the cable BC

    2. Relevant equations
    Since it is in equilbrium.
    [tex]\Sigma F = 0[/tex]
    [tex]\Sigma M = 0[/tex]

    3. The attempt at a solution
    The most confusing part for me, is moment about an axis. (If possible, please tell me, how to find moment about an axis - the direct method and through the vector matrix).

    Correct me, if i am wrong.

    rBC = 0.3i - 0.6j + 0.2k
    |rBC| = 0.7
    uBC = 1/0.7 (0.3 i - 0.6j + 0.2k)

    TBC = |TBC|/0.7 (0.3i - 0.6j + 0.2k)

    Now
    [tex]\Sigma Fz = 0[/tex]
    [tex] = -300 + Az + TBC(0.2 / 0.7)[/tex]
    Az is unknown, so to determine Az - we find moment about the x axis of B.
    This will give, Az = 0
    [tex]\Sigma Fz = 0[/tex]
    [tex]= -300 + TBC(0.2/0.7) = 0[/tex]
    TBC = 1050 N.

    [tex]\Sigma Fx = 0[/tex]
    Ax + 1050(0.3/0.7) = 0
    Ax = -450 N

    [tex]\Sigma Fy = 0[/tex]
    Ay - 1050(0.6/0.7) = 0
    Ay = 900N

    Thats what i could do max (i think im right), now only moment about Y-axis w.r.t a and moment about Z-axis is left, w.r.t a again. (May and Maz).
    Please tell me how to get this part, with 2-3 methods to get moment about an axis (Direct and through matrix).

    Thanks a lot =)
     

    Attached Files:

    Last edited: Jun 14, 2010
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted