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Angular velocity of ball-mass system

  1. Dec 11, 2006 #1
    1. The problem statement, all variables and given/known data
    A device consisting of four heavy balls connected by low-mass rods is free to rotate about an axle. It is initially not spinning. A small bullet traveling very fast buries itself in one of the balls. In the diagram, m = 0.004 kg, v = 450 m/s, M1 = 1.4 kg, M2 = 0.3 kg, R1 = 0.7 m, and R2 = 0.2 m. The axle of the device is at the origin < 0, 0, 0 >, and the bullet strikes at location < 0.228, 0.662, 0 > m. Just after impact, what is the angular speed?

    [​IMG]


    2. Relevant equations
    L=Iw
    Iinitial=(2/5)(2*[1.4*0.7^2]+2[0.3*0.2^2])
    Ifinal=(2/5)[1.404*0.7^2+1.4*0.7^2+2(0.3*0.2^2)]?
    Delta E=Delta(.5*I*w^2)

    3. The attempt at a solution
    I tried to use conservation of energy, where the Final E=Initial E, and just solve for Wfinal.. but the answer was wrong. I feel like I'm missing something.
     
  2. jcsd
  3. Dec 11, 2006 #2

    OlderDan

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    Science Advisor
    Homework Helper

    In collisions where things stick together, mechanical energy is not conserved. You need conservation of angular momentum.
     
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