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Homework Help: Please help with spring problem

  1. Feb 25, 2006 #1
    solved thanks to dicerandom... i forgot that vf is squared in the second formula. thanks so much
    Last edited: Feb 25, 2006
  2. jcsd
  3. Feb 25, 2006 #2
    Your approach sounds good, I think you probably just made an algebraic mistake somewhere along the way. Use conservation of momentum to find the velocity of the bullet+block system in terms of the bullet's initial velocity, then use conservation of energy to relate the velocity of the bullet+block to the displacement of the spring.

    Edit: Just for reference...

    Conservation of momentum: [tex]m_i v_i = m_f v_f[/tex]
    Kinetic energy: [tex]\frac{1}{2} m v^2[/tex]
    Spring potential energy: [tex]\frac{1}{2} k x^2[/tex]
  4. Feb 25, 2006 #3
    Looks like you forgot to square the velocity in you kinetic energy term.
  5. Feb 25, 2006 #4
    thanks alot :!!)
  6. Feb 25, 2006 #5
    My pleasure :smile:
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