Moment of Inertia of a Disk and mass

[drj1]

Homework Statement

Figure (a) shows a disk that can rotate about an axis at a radial distance h from the center of the disk. Figure (b) gives the rotational inertia I of the disk about the axis as a function of that distance h, from the center out to the edge of the disk. The scale on the I axis is set by IA = 0.010 kg·m2 and IB = 0.210 kg·m2. What is the mass of the disk?
Here's a link to the image --> http://www.webassign.net/hrw/10-35.gif

Homework Equations

Inertia=Icom + Mh^2
=(mL^2)/2 + Mh^2

The Attempt at a Solution

I set .010= (mL^2)/2 and solved for L^2 which turns out to be (.02/m). I then plugged this term into L^2 variable of the equation I=(mL^2)/2 + Mh^2. Then I plugged in .210 for I and .2 for h and solved for m which came out to be about 5.25. I thought I had it right but I don't. Help would be great I appreciate it.

 

[kuruman]

You know that at the edge of the disk the moment of inertia is 0.210 kg m² and that h = L = 0.2 m. Put everything in the parallel axes theorem and solve for the mass. You don't have to guess what the moment of inertia at h = 0 is.

 

[drj1]

Yes but in this case h does not equal L because the axis of rotation is not at the edge of the disk it is somewhere between the center of mass and the edge of the disk.

 

[drj1]

Oh okay I just read the problem over again and that makes sense now. Thanks a lot for your help.