Homework Help: Lab: Moment of Inertia

1. Dec 6, 2011

1. The problem statement, all variables and given/known data

Mass m will be varied between 50-110 grams, in 20 gram increments.

2. Relevant equations

I need to find the torques of each run (50, 70, 90, then 110 grams). I already have the electronically-collected data for the linear accelerations of the masses:

run 1: .050 kg, .1558 m/s/s
run 2: .070 kg, .2152 m/s/s
run 3: .090 kg, .2766 m/s/s
run 4: 1.10 kg, .3480 m/s/s

3. The attempt at a solution

I've been given a hint more or less. "Note: the tension in the string must first be determined from the acceleration data, then used to calculaate the torque on the system, given that the pulley on the rotary motion sensor has a radius of 15 mm."

Here's my attempt for the first one:

mg-T=ma
.050(9.8)-T=.050(.1558)
T=0.482
$\tau$=Fr
$\tau$=Tr
$\tau$=0.482(.015)=.00723 Nm

a=r$\alpha$
$\alpha$=a/r
$\alpha$=.1558/.015=10.39 rad/s2

Then I'm supposed to plot all four sets of data as points on a graph, calculate the slope, and thus find the moment of inertia of the disk and ring combination, since $\tau$=I$\alpha$

Is this the right way to go about it?