1. The problem statement, all variables and given/known data 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 2. Relevant equations T=2pi/w W=V/r 3. 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.