# CM and torque

#### Stryder_SW

1. Homework Statement
A thin 7.0 kg wheel of radius 32 cm is weighted to one side by a 1.0 kg weight, small in size, placed 25 cm from the center of the wheel.

(a) Calculate the position of the center of mass of the weighted wheel.
*edit* found the CM, its 3.125cm from the center *edit*
(b) Calculate the moment of inertia about an axis through its CM, perpendicular to its face.
*edit*SOLVED*edit*

2. The attempt at a solution
*edit*I realize I need to use the parallel axis theorem on part b, but I don't really understand how to apply it.*edit*

Last edited:
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#### tiny-tim

Science Advisor
Homework Helper
Hi Stryder_SW! (b) Calculate the moment of inertia about an axis through its CM, perpendicular to its face.

a nudge in the right direction would be greatly appreciated.
nudge nudge …

from the PF Library … Parallel axis theorem: the moment of inertia of a body about an axis is IC + md2

where m is the mass, d is the distance from that axis to the centre of mass, and IC is the Moment of Inertia about the parallel axis through the centre of mass.  #### Dr.D

Has your class talked about the parallel axis theorem? You have here two bodies, and it is not difficult to find the MMOI for each of them separately with respect to their own CM. Now you need to transfer that MMOI to their common CM and add them.

#### Stryder_SW

No, unfortunately my class fails at teaching physics. We tend to skip over these important theorems that make our lives so much easier.

#### Stryder_SW

I realize I need to use the parallel axis theorem, but I'm having a hard time applying it.

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