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Homework Help: Momentum and kinetic energy- pendulum component

  1. Apr 16, 2007 #1
    1. The problem statement, all variables and given/known data

    An 18-g rifle bullet traveling 230 m/s buries itself in a 3.6kg pendulum hanging on a 2.8-m-long string, which makes the pendulum swing upward in an arc. Determine the horizontal component of the pendulum's displacement.

    2. Relevant equations

    MaVa1 + MbVb1= MtVt2

    k.e.= 1/2mv^2

    p.e.= mgh

    3. The attempt at a solution

    I can find the velocity of the pendulum, but not the displacement:

    230 m/s * .018= 4.4 kg m/s

    4.4 kg m/s / 3.6018 kg = 1.15 m/s (speed of the pendulum with bullet after collision)

    I just dont know how to find the component of the horizontal displacement. Any help would be greatly appreciated.
  2. jcsd
  3. Apr 16, 2007 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Once you've got the speed of the pendulum you will know how much kinetic energy it has. Also you can assume the pendulm at its maximum arc displacement has traded all that kinetic energy for gravitational potential energy.
  4. Apr 16, 2007 #3
    230 m/s * .018= 4.14 kg m/s
    <did you miss 1 in 4.14?>

    use conservation of energy principle to find height, and then try drawing a diagram of the system @ its final position. Then you just need trigonometry to get the x component.
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