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Homework Help: Finding the reaction of a beam

  1. Apr 27, 2007 #1
    1. A Beam of negligible weight AB, carrying a mass of 70kg at its end B, is hinged to a vertical wall at A and held at B 30degrees to the vertical wall by a light cable BC of 5mm diameter, C is at a distance vertically above A

    Find the reaction of the beam at the wall and predict the behaviour of the cable by determining its Young;s Modulus if it is not allowed to extend more than 0.1% of its length under any condition

    2. Stuck on what equations i need to use for the above

    3. I drew the diagram in question and thats as far as i got =/

    http://img201.imageshack.us/img201/1646/problemib2.jpg [Broken]
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Apr 27, 2007 #2


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    Did you try to sum the moments about A?
  4. Apr 28, 2007 #3
    Sorry, i don't have any idea what you're talking about =/
  5. Apr 28, 2007 #4


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    Fred is talking about taking moment or torque about A, the second condition of static equilibrium.

    I would imagine you have to find the force along the cable and then use Hooke's Law in order to calculate the Young's Modulus or Modulus of elasticity.
  6. Jun 6, 2007 #5
    I still havn't been able to get my head round it.

    Thing is, i havn't been taught how to do it, therefore i don't understand the terms you are using.

    I need maybe a worked example of something similar that i can understand the forumla to use and the method of working it out.


  7. Jun 16, 2007 #6
    Go through the statics tutorials.

    http://web.umr.edu/~bestmech/ [Broken]
    Last edited by a moderator: May 2, 2017
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