A student sits on a rotating stool holding two 2 kg masses. When his arms are extended horizontally, the masses are 0.78 m from the axis of rotation, and he rotates with an angular velocity of 1.7 rad/sec. The student then pulls the weights horizontally to a shorter distance 0.25 m from the rotation axis and his angular velocity increases to omega2. For simplicity, assume the student himself plus the stool he sits on have constant combined momentum of inertia I(subscript s) = 1.8kg*m^2. Find the new angular velocity omega2 of the student after he has pulled in the weights. Answer in units of rad/s.
When the student pulls the weights in, he performs mechanical work - which increases the kinetic energy of the rotating system. Calculate the increase in the kinetic energy. Answer in units of J.
The Attempt at a Solution
I'm not sure of I*omega is the right formula, because it seems the moment of inertia stays constant throughout. So I'm stuck.