# Homework Help: Dynamics: Angular Acceleration of Rods Connected to Disk

1. Jul 9, 2011

### vercingortix

1. The problem statement, all variables and given/known data
Bars BC and AB and dish OA are attached by a pin like in the picture. The dish has a constant angular velocity $\omega\_{0}$. Find the angular acceleration of bars BC and AB.

2. Relevant equations
Relative Motion Equations:
v$_{b}$=v$_{A}$+v$_{A/B}$
a$_{B}$=a$_{A}$+$\alpha_{A}$Xr$_{B/A}$-$\omega^{2}$r$_{B/A}$

3. The attempt at a solution
So far, I have this written down:

V$_{A}$=$\omega$r
a$_{A}$=V$_{A}$$^{2}$/r=$\omega^{2}$r

a$_{B}$=$\alpha_{BC}$Xr$_{BC}$-$\omega_{BC}^{2}$r$_{BC}$

Still just fumbling over these equations. Any help is appreciated.

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Last edited: Jul 9, 2011
2. Jul 10, 2011

### tiny-tim

welcome to pf!

hi vercingortix! welcome to pf!

(have a theta: θ and an omega: ω )

(centripetal acceleration is irrelevant)

ω = (vP - vQ)/PQ

so find vB as a function of θ

3. Jul 10, 2011

### vercingortix

That equation looks foreign to me. What I'm currently trying to do is solve for angular acceleration of the bar by knowing the omega and accelerations of both A & B. Something like the second equation in my original post. I'm very lost.

4. Jul 11, 2011

### tiny-tim

hi vercingortix!

ω = |vP - vQ]/PQ

and

α = |aP - aQ|/PQ

are the definitions of angular speed and acceleration

so find the x,y components of B as a function of θ, and differentiate to get vB and aB

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