- #1
ChiHawksFan
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Homework Statement
Hi all,
I just had a quick question regarding a problem that I have to write a lab report on. The problem involves solving for the moment of inertia of a system that involves a pulley with a hanging mass attached to a spool that turns a flywheel. The solution is supposed to be in terms of the mass the hanging weight and the acceleration of the weight. In lab we were eventually given the equation that could be used to solve for the moment of inertia. It is as follows: I={[r2(mg-ma)]/α} My question involves how to derive this. I know that it is a sum of all forces problem, but I can't seem to get the right answer. Here is a link to the problem. It is on the second page and is titled "Moment of Inertia Problem".
Homework Equations
∑F=ma
∑τ=Iα
a=rα, α=a/r
mh = The mass of the hanging weight
Md = The mass of the disk, ring and spool configuration
r = the radius of the spool
The Attempt at a Solution
Here is a drawing I made of the situation:
My attempt at the solution is as follows:
∑Fy = mha
mhg - τ = mha
τ = mhg - mha
∑τ = Iα ----------> I = τ/α
I = (mhg - mha)/α
α = a/r
I = [r(mhg - mha)/a]
I am unsure where to get the other r from.
Thanks for any help!