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Upward force on beam

  1. Nov 14, 2004 #1
    A 3.0-m-long rigid beam with a mass of 100 kg is supported at each end. A
    80 kg student stands 2.0 m from support 1. How much upward force does support 1 exert on the beam?

    I first found the weight of the student to be 784N.
    so 784N*2cm =F*3cm
    F= 522.67N
    is this right?
  2. jcsd
  3. Nov 14, 2004 #2
    No, its not. I think you forgot to take the moment caused by the weight of the beam.
    I think this is how it should be done:
    (2x784)+(1.5x980) = 3xF
    This gives us the value of F(Force on the other support)=1012.67N
    Substracting this value from the total downward force(784N+980N) we get the upward force exerted by the support1 be 751.33N
  4. Nov 14, 2004 #3

    Yes, I forgot to consider the weight of the beam.
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