# Homework Help: Angular Acceleration of a Rigid Bar

1. May 20, 2013

### reuben19

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

Two identical masses with a mass of m each are connected by a rigid bar of negligible mass and rotate in a vertical plane in an anti-clockwise direction.

2. Relevant equations

If the system is released from rest when it is in a horizontal position, determine the angular acceleration of motion.

3. The attempt at a solution

So far, this is my progression towards a final solution. Firstly, find the moment of inertia of the system:

I=Ʃ(r^2)(m)
= (d-a)^2(m) + (a)^2(m)
= (d-a)(d-a)(m) + (a)^2(m)
= md^2 - 2adm + 2ma^2

I'm getting stuck after I do this, because I have no idea what to do after I find the moment of inertia in order to find the angular acceleration. I have attached an image to help the visualisation of the situation. Your help would be greatly appreciated! :)

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

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### Rigid Bar.png
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2. May 20, 2013

### TSny

Think about what causes the system to have an angular acceleration. Which way will it tend to rotate when you let it go? Why? What is the rotational analog of Newton's second law of motion?