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Bullet Momentum problem

  1. Jul 6, 2009 #1
    1. The problem statement, all variables and given/known data
    A 7.0-g bullet is fired into a 1.5-kg ballistic pendulum. The bullet emerges from the block with a speed of 200 m/s, and the block rises to a maximum height of 12.6 cm. Find the initial speed of the bullet.

    2. Relevant equations



    3. The attempt at a solution
    I used the equation:
    (Mbullet)(Initial Velocity)+(Mpend)(Initial Velocity)=(Mb)(Fvelocity)+(Mp)(Fvelocity)
    Once i plugged in all of the information i have i came to the answer of 306.5 but it is incorrect.
     
  2. jcsd
  3. Jul 6, 2009 #2

    Doc Al

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    Staff: Mentor

    Conservation of momentum applies to the collision of bullet and block, but how did you make use of the maximum height? (You'll need a second equation.)
     
  4. Jul 6, 2009 #3
    For my second equation i used (.5mvf^2)-(.5mvi^2)= -(mgyf-mgyi)
    when i solved: vf=.49
     
  5. Jul 6, 2009 #4

    Doc Al

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    Show exactly how you got that result.
     
  6. Jul 6, 2009 #5
    Initial V Of Pend= 0 Initial Height of Pend= 0
    so (.5)mvf^2= -mgyf
    masses cancel
    vf= square root[ (2)(g)(0.0126)]
    =.49
     
  7. Jul 6, 2009 #6

    Doc Al

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    Staff: Mentor

    12.6 cm = 0.126 m (not 0.0126).
     
  8. Jul 6, 2009 #7
    dang that was my problem lol. thanks
     
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