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Homework Help: Ballistic Pendulum Max Height

  1. Jan 16, 2009 #1
    1. The problem statement, all variables and given/known data

    A 16g bullet is fired into the bob of a ballistic pendulum of mass 1.5kg When the bob is at its maximum height, the strings make an angle of 60 degree with the vertical. The length of the pendulum is 2.3 m. Find the speed of the bullet.

    2. Relevant equations


    3. The attempt at a solution

    So I think it is an inelastic collision so vf = (mbullet*vbullet) / (mbullet+mblock)

    After collision:

    (1/2)*(mbullet+mblock)vf2 = (mbullet+mblock)*g*h


    then I solved for vf2=2*9.981*1.15=22.563

    the I substitute in to the first formula ( I actually squared both sides to use vf^2) to find vbullet= 346.2 m/s. However it is wrong. Where did I do wrong ??
  2. jcsd
  3. Jan 16, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Your method looks perfect. Check your arithmetic in your last step.
  4. Jan 16, 2009 #3
    Cool. I found out that I got the wrong mass for the last computation, I put in 1.15 instead of 1.5
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