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Homework Help: Mass on spring

  1. May 13, 2010 #1

    bon

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

    Mass m attached to spring with spring constant k=Am. It feels a resistive force magnitude Bmv where v is the speed. and A, B are constants such that 4A > B^2

    What is the fractional change in amplitude of oscillation in one complete oscillation?


    2. Relevant equations



    3. The attempt at a solution

    Ok so ive written down the DE:

    x'' + Bx' - Ax = 0 and solved..but this gives be Ce^-Lt + De^-L't where C, D, L and L' are constants...

    1) i dont see how this oscillates... 2) how do i work out fractional change in amplitude of oscillation?
     
  2. jcsd
  3. May 13, 2010 #2

    tiny-tim

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    Hi bon! :smile:

    (try using the X2 tag just above the Reply box :wink:)
    Nooo :redface:
     
  4. May 13, 2010 #3

    bon

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    Why not? I thought this was a direct consequence on NII (and cancelling the m)
     
  5. May 13, 2010 #4

    tiny-tim

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    One of the signs is wrong. :wink:
     
  6. May 13, 2010 #5

    bon

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    ok i see thanks i can now solve the eqn but how do i find fractional change in amplitude of oscillation
     
  7. May 13, 2010 #6

    tiny-tim

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    Well, what's your solution now? :smile:
     
  8. May 13, 2010 #7

    bon

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    not to worry - i get it now. thanks
     
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