Angular acceleration with a mass

[tg22542]

Homework Statement

1) A solid cylinder of mass M = 1.54 kg and radius r = 0.100 m pivots on a frictionless bearing. A string wrapped around the cylinder pulls downward with a force F that equals the weight of a 0.590 kg mass, i.e., F = 5.782 N. Calculate the angular acceleration of the cylinder.

2)If instead of applying the force F, a mass m = 0.590 kg is hung from the string, what is the angular acceleration of the cylinder?

Homework Equations

The Attempt at a Solution

I found the answer to 1) to be 75.1 rad/s^2.

For 2) I have been doing this:

m*g*r = T

angaccel = t/l

Inertia moment for a solid cylinder = 1/2mr^2

angaccel = t / 1/2mr^2

using my numbers that gives me:

(.5782)/(.5*1.54*.1^2) = 75.091 rad/s^2

This is wrong. I have tried 8 times now on the same question and cannot get it, any help?

 

[CWatters]

Hint: Since the 0.590Kg mass is accelerating downwards the tension it generates isn't mg.