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Raziel2701
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Homework Statement
A uniform circular turntable of mass 2m and radius R is at rest in space. Koko throws a lump of putty of mass m and speed v toward the edge of the turntable so that it sticks at the extreme edge of the turntable at R.
Using conservation of L, show that the angular velocity ω of the putty/turntable system after the collision is [tex]\omega=\frac{2v}{5R}[/tex]
Homework Equations
Parallel-axis theorem. Conservation of angular momentum
The Attempt at a Solution
I found the center of mass of the putty/turntable system to be R/3. I set my origin to be there. For the initial angular momentum, that is before the putty sticks to the turntable, I get mv2R/3.
For the final angular momentum I get the moment of inertia times the angular velocity. My problem is in determining what the right moment of inertia is.
Why can't I just use the parallel axis theorem applied to the putty and the turntable to find the moment of inertia? I've done mR^2 for the putty, plus 4/9mR^2 by the parallel axis theorem, plus another mr^2 from the disk(since it's mass is 2, the half cancels) plus 1/9 mR^2 by the parallel axis theorem?
So why is this wrong though?