Work / Moment of inertia

1. Feb 20, 2008

PeterPoPS

1. The problem statement, all variables and given/known data
A man is standing on a rotating plate (rotates without friction). In case A he is hold 1weight in each hand (straight out) with the mass m and he is rotatin with angular velocity omega_0.
Then he moves his arms down so they are parallell to the body (case B) and increases his angular velocity to omega_1.
Calculate the new angular velocity omega_1 and the work U which the man must do to change his body configuration to case B.
You can assume that the moment of inertia on z-axis for the man is I_0 in case A and I_0 / 2 in case B.
The length of the arms of the man is l, so each weight are l units out in case A and lowered l units (and ofcourse moved l units toward the body) in case B.

omega_1 = 2 omega_0
and
U = 0.5*I_0*(omega_0)^2 - 2mgl

My Problem is i get how to calculate the angular velocity omega_1
But I don't understand how to even start on calculating the work done.

Best regards /Peter

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution