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Homework Help: Help finding radius for the torque

  1. Dec 16, 2012 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    Torque = Force * radius * sin(angle)

    3. The attempt at a solution


    I am trying to find the radius for the torque of the cable, but I can't seem to use any trig to solve for that side in terms of L.
  2. jcsd
  3. Dec 16, 2012 #2
    The radius is L,
    you do not need any trigonometry.
    remember, radius (when referring to torque) is defined as the distance from the pivot point to the point that the force is acting on - in other words - L.
  4. Dec 16, 2012 #3
    The pivot point to the point that the force is acting on is marked in my diagram by 'R'. I don't see how R = L
  5. Dec 16, 2012 #4
    The wire is pulling on the beam with a tension, this is the force in question. The point that you have marked as the point that the force is acting upon is on the wire itself. In order to cause a torque on the beam the force must be acting on the beam itself, not the wire.
  6. Dec 16, 2012 #5
    I don't understand what you are saying. The force of the Tension is acting on the beam. The axis of rotation is the hinge. So, we need the distance from the Tension to the axis of rotation. To do that, we use the perpendicular distance created from the axis of rotation to the Tension. Isn't that what we want?
  7. Dec 16, 2012 #6


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    You have a right triangle where L is the hypotenuse and R is the side opposite the 30-degree angle. What trig function relates side opposite and hypotenuse?
  8. Dec 16, 2012 #7
    Ah, I see the sine function now. Thanks
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