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Homework Help: Mass of a child on a seesaw

  1. Oct 11, 2008 #1
    1. The problem statement, all variables and given/known data
    Two children balance on a seesaw. One, with a mass of 30 kg, is seated 2.0 m from the pivot. The other is seated 2.5 m from the pivot. What is the mass of the second child?

    2. Relevant equations

    3. The attempt at a solution
    I drew the diagram of the two children and I found the force of gravity acting on the first child:
    Fg=mg ; Fg=(30 kg)(9.8 m/s/s) ; Fg = 294N

    I know that the Net Force would be 0 because the seesaw is balanced.
    And then...I dont know what to do...
  2. jcsd
  3. Oct 11, 2008 #2
    Okay, so they both have the same acceleration acting on them [tex] g = 9.81ms^{-1} [/tex]

    However they both have torques created by the distance from the pivot point.

    We know that [tex] \tau = Fr [/tex]

    So we're saying that [tex] (30)(9.8)(2.0) = (m)(9.8)(2.5) [/tex]
  4. Oct 11, 2008 #3
    ohh okay! and then you would just isolate and...yaa! Thanks so much for your help!! I really really appreciate it!!!!
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