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Conservation of energy - spring

  1. Apr 4, 2014 #1
    1. The problem statement, all variables and given/known data
    hh86igL.png
    Hello, I'm having a problem with this. So we drop the weight on this spring, and the question is: how much does the spring compress? The mass is 5kg, the height 0,4m, and the spring elasticity factor k=1700N/m.

    2. Relevant equations



    3. The attempt at a solution
    I've tried to equalize the potential energies of when we drop the weight, and when it's all the way down. It looks like this: m(h+ΔL)=(1/2)*k*(ΔL)^2. I get a quadratic equation, and solve it. I get two answers one with +, and one -. I've tried to enter the positive one, and it's not correct. Should I enter the negative one, or is my whole attempt faulty?
     
  2. jcsd
  3. Apr 4, 2014 #2

    PhanthomJay

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    Looks like you left out g in your gravitational PE term, otherwise, looks good. Think positive.
     
  4. Apr 4, 2014 #3
    Should it be g*m*(h+∆L)=(1/2)*k*(∆L)^2, because if it's on both sides it's the same
     
  5. Apr 4, 2014 #4

    PhanthomJay

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    Sure!
     
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