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Basic Questions

  1. Mar 17, 2009 #1
    Here is a very basic question that I need help with.

    1. The problem statement, all variables and given/known data
    A spring has a spring constant (k) of 82 N/m. How far must the spring be compressed to store 35J of potential energy?


    2. Relevant equations
    I think it is: E = 1/2 kx^2

    3. The attempt at a solution
    I don't understand how to setup this problem. Please help me.
     
  2. jcsd
  3. Mar 17, 2009 #2

    LowlyPion

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    Welcome to PF.

    Let's see. You have the equation. They tell you what E is. They tell you what k is ... so you're having trouble solving for x?
     
  4. Mar 17, 2009 #3
    yes.
    should the equation look like this?
    35J = 1/2 (82 N/m) x^2
     
  5. Mar 17, 2009 #4

    LowlyPion

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    Just solve for X.
     
  6. Mar 17, 2009 #5
    I don't know how to.
    is 82 N/m the same as 82 J?


    would I get

    35J divided by 41 N/m = x^2? then x = square root of 35J divided by 41 N/m?
     
  7. Mar 17, 2009 #6

    LowlyPion

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    No N/m is a spring constant. It moves 1 meter for every 82 Newtons of force.

    Joules are units of what? N-m? and you are dividing by N/m? that yields m2 and x2 is m2 ... so everything is right.

    As to your calculation ... that's right.
     
  8. Mar 17, 2009 #7
    i dont know whAt to do
    plaese show me exactly how to solve this problem and all the steps i am so lost
     
  9. Mar 17, 2009 #8

    LowlyPion

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    Look. You've already solved it ... that is if you meant to divide 35 by 41 before you took the square root.
     
  10. Mar 17, 2009 #9
    i just want an answer in meters.
     
  11. Mar 17, 2009 #10

    LowlyPion

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    That gives you an answer in meters.
     
  12. Mar 17, 2009 #11
    (sqaure root of 35j divided by 41 N/m) meters?
     
  13. Mar 17, 2009 #12

    LowlyPion

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    sqaure root of (35j divided by 41 N/m) meters?

    Yes. I already showed you that you get m2 before you take the square root.
     
  14. Mar 17, 2009 #13
    thanks for your help, but i still cant understand this, i'll have to ask my instructor.
     
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