# Angular velocity of ball-mass system

1. Dec 11, 2006

### smedearis

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?

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. Dec 11, 2006

### OlderDan

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