Angular Momentum of circular disk

[rms830]

Homework Statement

A flat uniform circular disk (radius = 2.50 m, mass = 1.00 102 kg) is initially stationary. The disk is free to rotate in the horizontal plane about a frictionless axis perpendicular to the center of the disk. A 55.0 kg person, standing 1.55 m from the axis, begins to run on the disk in a circular path and has a tangential speed of 2.20 m/s relative to the ground.

Homework Equations

I have been using the definition of angular motion equation (L = I*omega)(I = mr^2) to try and find the resulting angular speed. What I am having trouble with is how to find L using the given numbers. I thought i read that L = r2, but putting those numbers into the equation has not given me the correct answer. The problem asks me to find the resulting angular speed, but since I have not been able to find L or omega, I haven't been able to solve.

Thanks.

 

[Doc Al]

Hint: Angular momentum is conserved. What's the initial angular momentum of the system before the person begins running?