How Does Shrinking Affect the Rotation Speed of a Planet?

[jim the duke]

Homework Statement

Planet A (at X meters) completes 1 full rotation (Y sec). Planet A then shrinks to (X2 meters)
What is its rotation speed now.
Conservation of angular momentum

Homework Equations

T=2pi/w
W=V/r

The Attempt at a Solution

I found how to reverse engineer the whole system but I'm unable to calculate w for a reduced radius.

 

[SteamKing]

What's the formula for calculating angular momentum?

 

[jim the duke]

SOLVED!
I used V1 x R1 / R2 = V2 then used the velocity of V2 against the circ of Planet A's new radius to give the answer, yipee!

 

[jim the duke]

oops!