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Find Maximum mass with the principles of torque and rotational equilibrium

  1. Nov 22, 2011 #1
    I need help with this physics problem! Please help I'm completely stuck.

    A beam 3m long is free to pivot up and down about the end attached to a wall. The mass of the beam is 25 kg and the cable supporting the beam can support a maximum force of 1800 N. What is the maximum mass that a man standing on the end can have before he snaps the cable. The angle of elevation between the cable and the beam is 30 degrees.
    ?






    I tried converting the 25 kg to newtons, therefore getting me 245N and subtracting that from the 1800 (which I thought would be the easy way) and then dividing by 9.8 to get the mass in kg, but that ended up being incorrect.

    The correct asnwer is 79.3 Kilograms, but I would enjoy to know how to get to that conclusion.
     
  2. jcsd
  3. Nov 23, 2011 #2
    You are almost correct except one thing, you forgot the angle of the cable relative to the beam.

    redo your equation by summing the forces in the Y direction (1800N is not in the Y direction)
     
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