## Rotating Chair

A physics student is sitting on a frictionless platform that is rotating with an angular speed of ωi = 3.3 rad/s. His arms are outstretched, and he is holding a heavy weight in each hand. The moment of inertia of the student, the extended weights, and the platform about the rotation axis is Ii = 8.1 kg*m^2. When the student pulls the weights inward toward his body, the moment of inertia decreases to If = 3.7 kg*m^2.

What is the resulting angular speed, ωf, of the platform?

What is the resulting angular speed, ωf, of the platform?

**By how much is the kinetic energy of the system increased? (Think about where this increase in energy comes from!)****7.22 rad/s**

**5.24×101 J**## Discussion

**NEW**

**part 2**

shouldn't the answer be 0kg*m^2*rad/s^2, since kinetic

energy is conserved?

**NEW**

**Re: part 2**

Try calculating the difference between rotational KE final

and rotational KE initial, where both are 1/2*I*w^2.