# Homework Help: Vector Mechanics, Interpretation of Problem

1. Jun 5, 2012

### c.teixeira

Hi there.

I am an Aerospave Engineering student, revisiting Vector Mechanics. My course recommended text book is "Vector Mechanics of Enginners, from Beer and Johnston". However, I have been complemeting with another book - " Methods of Analytical Dynamics, from Meirovitch". This book, treats Analytical Mechanics, which is beyond the scoop of my course. However, I am just reading the chapters concerning Motion relative to Rotating frames of reference and Rigid Body Dynamics.

Now, the Meirovitrch text book is way more theotytical. but I gave it a lot of time to correcclty interpert the subject. The thing is, sometimes, when I try to apply the Meivotich equations to the Beer and Jonhston multiple exercices, the results are incorrect! I feel rather frustrated, since I don't now why!

For example, in the attached file, there is on of those exercices I am refering.

If I assume there is a Reference Frame rotating with ω1, I can then compute the velocity and acceleration of point A correctly using the expressions given in the Meirovitch. (second attached file). In this case, the relative velocity of point A is ω2 * r.

However, if I imagine a Reference Frame Rotating with an angular velocity Ω = ω1 + ω2, then there would be no relative motion of the point A. The results(both the velocity and aceleration) using this rotating frame are incorrect. But, shouln't it work? I have carefully looked at the meirovith deductions, and I think it should!

Greatfull for any help!

Regards

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