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Homework Help: Conservation of Momentum Law- Recoil Velocity (Question)

  1. Jan 19, 2009 #1
    First time posting, I hope I do this correctly!

    I am struggling to grasp this concept. This is my attempt at solving. If I am completely off base, will some explain to me again how it works. Our instructor explained it to us with a very detailed formula which, I must confess, has caused me more than a little anxiety because I am not following! Thanks for the help!

    1. Rifle (suspended by strings) - 2kg; fires bullet of 0.01 kg at speed of 200 m/s. What is the recoil velocity of the rifle?

    2. (mv) + (mv) = (M + m)(v)

    3. (0.01)(200) + 0 = (0.01 +2)(v)
    divide both sides by 2.01, and the answer is v= .99

    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    Last edited: Jan 19, 2009
  2. jcsd
  3. Jan 19, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    This isn't quite right.

    Momentum is conserved. What's the total momentum of the system (rifle + bullet) initially? What's the total momentum of the system after the bullet is fired?

    Set that total momentum equal to m1v1 + m2v2.
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