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Homework Help: Block and the bullet

  1. Apr 9, 2015 #1
    1. The problem statement, all variables and given/known data
    Which equation could adequately be used to determine how high the block goes after being hit by the bullet (a height h)? (see figure)


    2. Relevant equations
    PE of spring = 1/2ks(s^2 final - s^2 initial)

    3. The attempt at a solution

    Based off of the equations, I believe the answer should be the second equation. I don't understand what else it could be..

    I have only one attempt

    Attached Files:

  2. jcsd
  3. Apr 9, 2015 #2


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    Some of the variables in those equations need to be definrd for us.

    I see L1, m, v, and h in the figure.

    What are k, s, M, V, an s without k ? Is that ks rather than k⋅s ?
  4. Apr 9, 2015 #3
    Maybe you could explain why you think it couldn't be the other two equations you excluded?
  5. Apr 9, 2015 #4
    Because the other two equations are missing components to their equations
  6. Apr 9, 2015 #5
    1/2ks(s^2 final - s^2 initial)

    ks = spring constant (k_s_)
    (s^2 final - s^2 initial) = final stretch - initial stretch
    v= velocity
  7. Apr 9, 2015 #6
    And what components do these two equations have that are missing that the other one isn't?
  8. Apr 9, 2015 #7
    (m+M)gh+ksh=1/2(m+M)V^2 the spring constant should be 1/2ksh^2 not ksh
    (m+M)v+ksh=(m+M)V Ugrav should be (m+M)gh instead of velocity multiplying the masses (m+M)v, also (m+M)V is missing V^2
  9. Apr 9, 2015 #8
    I think you have your answer then.
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