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Homework Help: Collisions of rocks in space

  1. Apr 1, 2008 #1
    1. The problem statement, all variables and given/known data

    In outer space a rock with mass 4 kg, and velocity < 4000, -2800, 3400 > m/s, struck a rock with mass 18 kg and velocity < 250, -290, 260 > m/s. After the collision, the 4 kg rock's velocity is < 3600, -2300, 3900 > m/s.
    What is the final velocity of the 18 kg rock?

    2. Relevant equations

    Momentum Principle

    pf = pi + Fnetdeltat

    3. The attempt at a solution

    Please help me if you can! Im pretty frustrated with this problem and I dont know why Im getting it wrong! I used the momentum principle, but it hasnt worked since this is a collision problem. Should I use that the final speed for the 18kg rock is v2f = 2(m/M)v1i

    v2 being the final velocity of 18kg
    v1 being the initial velocity of 4kg
  2. jcsd
  3. Apr 1, 2008 #2
    Hi, Write the velocities in vector form. Like for 4 Kg rock, initial velocity will be


    Then apply

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