Rotation problem: which would stop first?

[Misako]

Hey! I'm new here in PF and is wanting to solve this teeny bitsy problem about rotation. I'm at 9th grade and is a newbie at physics. :p

Homework Statement

Two razor fans, one larger and one smaller, were turned on at the same time and turned off at the same time.

Question: which fan would stop first? the larger one or the smaller one?

Homework Equations

I'm thinking of: angular velocity = delta s/ r x delta t

The Attempt at a Solution

I need to prove the answer by using an equation. So the equation must include probably a radius(for the smaller and larger blade) and the time. Problem is, i can't seem to find that and is stumped. But for me, I really think the smaller fan would stop first.

Halp? =(

 

[Redbelly98]

Welcome to PF.

Has torque been discussed in your class?

 

[tiny-tim]

Welcome to PF!

Hi Misako! Welcome to PF!

hmm … that seems rather difficult for 9th grade …

let's assume they're turning at the same angular rate …

what is the initial energy proportional to, r r² or r³?

and what is the rate of energy loss proportional to?