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Finding the tension and components

  1. Feb 16, 2008 #1
    The horizontal beam in the figure below weighs 140 N, and its center of gravity is at its center.


    Find the tension in the cable.

    Find the horizontal and vertical component of the force exerted on the beam at the wall.

    How would I solve this?
  2. jcsd
  3. Feb 16, 2008 #2
    You'll have to use Newton's second law, and Newton's second law for rotation (that is, the torque equation). Note that the beam is in equilibrium, so what can you say about its translational and angular acceleration? Also, you'll want to start by identifying all of the forces on the beam (Hint: There are 5 forces.) Drawing a free body diagram for the forces and for the torque will help you greatly.
  4. Feb 16, 2008 #3
    the formula is t(net external)=I(moment of inertia) x a (angular acceleration). i still don't know how to identify and plug in the values.
  5. Feb 16, 2008 #4
    You should know that Newton's second law [tex] \vec{F}_{NET} = m\vec{a} [/tex] breaks down into:

    [tex] F_x = F_1 + F_2 = 0 [/tex]

    [tex] F_y = F_3 + F_4 + F_5 + F_6 = 0 [/tex]

    Now all you have to do is identify what these components are.

    And you should know that to find the net torque, you simply add the torques due to each force. To make life simple, take the torque about the right end of the beam. If we take counter clockwise to be positive, you'll have:

    [tex] \tau_{NET} = F_7(R_7) - F_8(R_8) + F_9(R_9) = 0 [/tex]

    One of these torques will go to zero. Taking the coordinate system into account, it will be the torque caused my F9. Why is this? Again, you would do well to make a free body diagram. One for the forces, and one for the torques.
    Last edited: Feb 16, 2008
  6. Feb 16, 2008 #5
    can you solve it for me, step by step with the correct answer.. so i can understand what your talking about and using the same strategy for the next 5 problems.
  7. Feb 16, 2008 #6
    If I solve it for you, you won't learn anything. But I'll gladly help you work through it. The first step would be drawing a free body diagram, and identifying all of the forces. Here's a hint to get you started: There are five forces, two of them act at the hinge of the beam. Can you tell me what these five forces are, and in which direction they act?
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