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Impact loading: Pogo stick

  1. Aug 10, 2011 #1
    1. The problem statement, all variables and given/known data

    http://i.imgur.com/CnAcu.png

    2. Relevant equations

    So, I'm having trouble figuring out how to start this problem.

    I'm trying to use this equation:

    Fe = W(1+[itex]\sqrt{1+2h/\deltast}[/itex]

    and [itex]\delta[/itex]st = W/k

    3. The attempt at a solution

    This is my attempt at summing the forces:

    [itex]\Sigma[/itex]F = 100 lbf/in * [itex]\delta[/itex] + Weight of child


    Thanks
     
    Last edited by a moderator: Aug 14, 2011
  2. jcsd
  3. Aug 12, 2011 #2

    PhanthomJay

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    You should first calculate the spring deformation under 400 pounds of max force in the spring, using Hooke's law. Then use conservation of energy equation.
     
    Last edited by a moderator: Aug 14, 2011
  4. Aug 14, 2011 #3

    nvn

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    danief: Your relevant equations are correct; and they are not a function of maximum deflection. You can change your approach as PhanthomJay suggests; or you can instead just use the approach you already started writing in your relevant equations, as follows.

    First, convert everything to a coherent measurement system. Next, the problem statement gives you h = 0.1016 m, Fe = 1779.2886 N, and spring constant k. Now simply solve your relevant equation for weight W. You are done.

    (By the way, ignore your attempt at summing forces in part 3 of post 1, which is incorrect.) Also, please do not post wide images directly to the forum page. Just post a text link to wide images.
     
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