# Find Angular Momentum

1. Jul 13, 2009

### shangri-la89

1. The problem statement, all variables and given/known data
A small puck of mass 36 g and radius
25 cm slides along an air table with a speed
of 1.9 m/s. It makes a glazing collision with a
larger puck of radius 59 cm and mass 85 g (ini-
tially at rest) such that their rims just touch.
The pucks stick together and spin around af-
ter the collision.
Note: The pucks are disks which have a
moments of inertia equal to 1/2mR^2.
What is the angular momentum of the sys-
tem relative to the center-of-mass after the
collision? Answer in units of kgm2/s.

2. Relevant equations
L=Iw
w=V/r
Torque=I*alpha
L=RxP

3. The attempt at a solution
To be honest I have no idea. I tried several obviously ill-fated attempts. I have found the center of mass, and I know that it has to do with crossing the initial linear momentum with the new radius... I think...

Any help would be greatly appreciated.

2. Jul 14, 2009

### tiny-tim

Welcome to PF!

Hi shangri-la89! Welcome to PF!

(have an alpha: α and an omega: ω and try using the X2 tag just above the Reply box )

(oh, and it's a grazing collision … a glazing collision is when you walk into a glass door! )

What is the angular momentum of the system before the collision?