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Homework Help: Finding the unstretched length of a bungee cable

  1. Oct 18, 2012 #1
    Two men both weighing 150lb jump off a bridge using a bungee cord with stiffness k=80lb/ft. One of the men is attached to the cable and plans to release the other man when they reach the water 120ft below the bridge. Once there the connected man will let go of the unconnected man when they touch the water. Determine the unstretched length of the cord. Also determine the maximum acceleration of the attached man and the maximum height he reaches above the water when he springs back up.

    2. Relevant equations
    T1 + ƩU = T2

    Us = 1/2 k (s)^2

    3. The attempt at a solution

    I used mgh for U and got an unstretched length of 90ft, but I'm not sure if it's correct and I dont know how to approach the kinematics of the second portion.
  2. jcsd
  3. Oct 19, 2012 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    It helps if you show us your reasoning and not just your answer.
    For the second part - why not just use conservation of energy again?
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