Calculating Final Angular Speed of Rotating Table

[gamer1319]

Homework Statement

a 40kg duck walks from the outside to the inside of a rotating circular table of mass 100kg. if the rotational intertia of the table is 250kg*m^2 and the duck moves from a radius of 2.5m to 1.5m, find the final angular speed of the table if it rotates at 2.0rad/sec at the moment the duck begins to move.

THANKS! I'm studying for a test and i can't do this question

Homework Equations

The Attempt at a Solution

what i did:

L = 250kg * m^2
Wf = ?
Wi = 2 rad /sec
r = 1.5 m

i don't know what to do from here

 

[rock.freak667]

You'll need to apply conservation of angular momentum given by Iω.

You should also know that for a point mass, like the duck, its inertia at some distance r is mr². So you need to get I for the table+duck system.

Then just apply the conservation law.