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Please help me =D

  1. Apr 29, 2009 #1
    A 35.0-g bullet strikes a 4.7-kg stationary piece of lumber and embeds itself in the wood. The piece of lumber and bullet fly off together at 8.0 m/s. What was the original speed of the bullet?
    I don't know where to begin...
     
  2. jcsd
  3. Apr 29, 2009 #2
    This one too pleeasee

    A thread holds a 1.5-kg and a 4.50-kg cart together. After the thread is burned, a compressed spring pushes the carts apart, giving the 1.5 kg cart a speed of 27 cm/s to the left. What is the velocity of the 4.5-kg cart?



    I would be so grateful if someone could help me..
     
  4. Apr 29, 2009 #3

    rl.bhat

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    Just go through the conservation of linear momentum.
     
  5. Apr 29, 2009 #4
    Hi there. Is conservation of linear momentum something you have studied in class? :smile:

    Also: I would start a new thread for each problem, else things get confusing/messy.
     
  6. Apr 29, 2009 #5
    Yes, im in the ib program but i was absent for that lesson..
    ha thanks for the heads up, i just started this
    Andd thank you both for the help
     
  7. Apr 29, 2009 #6

    Okay, well paraphrasing Conservation of momentum says that if no external forces act on a system (which is true in this case), then the total linear momentum is conserved.

    That is, [itex]\sum mv_{initial}=\sum mv_{final}[/itex]

    In this case,

    [tex]M_{bullet}V_{bullet}+M_{block}V_{block}=M_{(block+bullet)}V'_{(block+bullet)}[/tex]

    where I used the ' symbol to indicate velocity after the collision

    And Yes, they are both conservation of momentum.
     
    Last edited: Apr 29, 2009
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