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Spring problem

  1. Nov 1, 2015 #1
    1. The problem statement, all variables and given/known data

    A bloc of 0,2 kg is attached to a spring on a horizontal surface with no friction. (The other side of the spring is attached to a wall, so it doesn't move) The spring constant is 5 N/m. If we pull on the spring, we move it by 0,12 m from its natural position and we let it go after that (It has an initial speed of 0 m/s) What is the speed when we have a maximal compression
    2. Relevant equations
    U=1/2*k*e^2
    Kf+Uf=Ki+Ui

    3. The attempt at a solution

    I get the following equation : 0,2v^2 + 5e^2 = 0,072

    I don't know what is the maximal compression !
     
  2. jcsd
  3. Nov 1, 2015 #2

    gneill

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    Staff: Mentor

    If the compression is maximal, how much more compression can there be? :wink:
     
  4. Nov 1, 2015 #3
    Well 0...
     
  5. Nov 1, 2015 #4

    gneill

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    Staff: Mentor

    Right. So in that instant, what is the block doing? Can it continue to move to compress the spring?
     
  6. Nov 1, 2015 #5
    At that moment, the spring is pushing against the bloc to the right. I just don't know what is the position at the maximum. I know tha tmy natural position is 0.
     
  7. Nov 1, 2015 #6

    gneill

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    Staff: Mentor

    Yes, but what is the block doing in that instant?
     
  8. Nov 1, 2015 #7
    Ehhhhh... I think it has something do with speed ?
     
  9. Nov 1, 2015 #8

    gneill

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    Staff: Mentor

    Yes. Think it through. The block moves, compressing the spring until it can't compress it any further. That's maximal compression. So the block's speed at that instant is...?
     
  10. Nov 1, 2015 #9
    It's 0 ? But I don't understand why...
     
  11. Nov 1, 2015 #10

    gneill

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    Okay, here's an analogy. You throw a ball straight up in the air. What is the speed of the ball when it reaches is maximal height?
     
  12. Nov 1, 2015 #11
    Its gooing to be 0 because the ball needs negative speed to go down.
     
  13. Nov 1, 2015 #12

    gneill

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    Staff: Mentor

    So when the block reaches the maximal compression of the spring...
     
  14. Nov 1, 2015 #13
    OH LOL ! WHen its at the maximum it doesnt move anymore !!!!!!!!!!!!!!!!!!!!!!! I guess that me and my brain who are tired today ! thank you!
     
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