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Homework Help: Momentum and Energy problem, conservation.?

  1. Mar 17, 2013 #1
    1. The problem statement, all variables and given/known data

    A pendulum of 9.99 kg is initially at rest, just skimming the floor below. A bullet of mass 0.01kg is fired at the bob. The bullet collides with the bob and embeds itself, after which the pendulum begins to move. The bullet-bob pendulum reaches the maximum vertical displacement of 4.60 cm.

    a) Calculate the velocity of the bullet just before the impact with the bob. (ANS: 949m/s)

    b) If a rubber bullet of mass 0.01kg was fired at the 9.99 bob with a speed of 949 m/s, and collided elastically with the bob, how high would the pendulum now rise?

    ANS b: 18.4 cm

    2. Relevant equations

    P1 = P2 and E1 = E2

    3. The attempt at a solution

    a) I think we are supposed to use the conservation of momentum and energy to answer this but I cannot do it.

    26 minutes ago - 4 days left to answer.
    Last edited by a moderator: Mar 17, 2013
  2. jcsd
  3. Mar 17, 2013 #2


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    Staff Emeritus
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    You're right. You need to use conservation of momentum and energy. Show us your attempt at applying those principles.
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