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I need help with a spring problem

  1. Oct 22, 2009 #1
    Please help me out, I'm new here, and I only have one more attempt on this problem, totally lost.

    1. The problem statement, all variables and given/known data

    A(n) 142 g ball is dropped from a height of 62.2 cm above a spring of negligible mass. The ball compresses the spring to a maximum displacement of 4.35501 cm. The acceleration of gravity is 9.8 m/s^2 . Calculate the spring force constant k. Answer in units of N/m.

    2. Relevant equations
    F=-kx


    3. The attempt at a solution
    mgh=-kx
    (.142)(9.8)(.622)=-k(0.435501)
    k=19.875

    ???
     
  2. jcsd
  3. Oct 22, 2009 #2
    You're setting energy equal to force. Instead of the force of the spring, use the potential energy of the spring.
     
  4. Oct 22, 2009 #3

    rl.bhat

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    Homework Helper

    Hi irbombardmnt, welcome to PF.
    Your relevant equation is not correct. mgh is the fall of potential. kx is not the energy.
    What is the formula for the energy stored in a stretched spring?
    In fact ball falls through h+x distance before it comes to rest.
     
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