Conservation of angular momentum, stuck on a problem

[yodachoda87]

Homework Statement

A student sits on a rotating stool holding two 2.0 kg objects. When his arms are extended horizontally, the objects are 1.0 m from the axis of rotation, and he rotates with an angular speed of 0.75 rad/s. The moment of inertia of the student plus stool is 3.0 kg·m2 and is assumed to be constant. The student then pulls the objects horizontally to 0.40 m from the rotation axis.

Homework Equations

Initial moment of inertia * initial angular velocity = Final moment of inertia * Final angular velocity

The Attempt at a Solution

My attempt was to find the moment of inertia of the stool/student only by taking 3.0kgm^2 minus mr^2 minus mr^2. The total system is the stool + two objects + student.

 

[Stonebridge]

The initial moment of inertia of the system is 3.0kg.m2 plus the two objects of mass 2kg at a distance 1m from the axis.
The final moment of inertia of the system is 3.0kg m2 plus the two objects at a distance 0.4m from the axis.
You are correct that the moment of inertia of each of the objects is mr²
You are also correct that
Initial moment of inertia * initial angular velocity = Final moment of inertia * Final angular velocity
from which you can find the final angular velocity.
[I'm guessing that was the question]