Finding New Rate of Rotation for a Student on a Rotating Platform with Dumbbells

[chess10771]

Homework Statement

A student stands on a platform that is free to rotate and holds two dumbbells, each at a distance of 65 cm from his central axis. Another student gives him a push and starts the system of student, dumbbells, and platform rotating at 0.95 rev/s. The student on the platform then pulls the dumbbells in close to his chest so that they are each 22 cm from his central axis. Each dumbbell has a mass of 5.00 kg and the rotational inertia of the student, platform, and dumbbells is initially 7.40 kg · m2. Model each arm as a uniform rod of mass 3.00 kg with one end at the central axis; the length of the arm is initially 65 cm and then is reduced to 22 cm. What is his new rate of rotation?

Homework Equations

Newtons 2nd law?

The Attempt at a Solution

Not really sure how to go about solving, Please show all work if possible, thanks in advance.

 

[TVP45]

I'd guess you're in a freshman physics class this semester, probably about Chapter 8, +/- 1 Chapter. So, what are you studying that looks anything like this? Skim through the text and look for a picture or diagram that suggests anything close to this.