Understanding solution method for finding accelerations in a mechanical linkage

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Homework Help Overview

The discussion revolves around understanding the application of equations for finding accelerations in a mechanical linkage system. Participants are comparing different approaches to the same problem, specifically regarding the use of angular acceleration in their calculations.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to reconcile their equation for acceleration with one found in Chegg, questioning the neglect of the cross product in the latter's approach. Other participants raise concerns about the justification for assuming zero angular acceleration in the context of the problem.

Discussion Status

The discussion has progressed with some participants providing insights into the implications of constant velocities leading to zero angular acceleration. The original poster acknowledges a realization about the importance of reading the problem statement carefully.

Contextual Notes

Participants note that the problem does not explicitly state a static situation, leading to confusion regarding the assumptions made about angular acceleration. The mention of constant velocities is highlighted as a critical piece of information affecting the interpretation of the problem.

whitejac
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Homework Statement


I was checking my work and Chegg uses the equations differently. Can somebody tell me why? Maybe I'm misunderstanding how/why to use the equation I chose.
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Steps 4-5.JPG

Homework Equations


They say aB = -ω2ABRB/Ai
I used aB = aA + αk x r - ω2rB/A

The Attempt at a Solution


So obviously mine will be a different answer, I only found aB but it gave me an i and j component because of that cross product. Which one is correct and why? Why can they neglect the cross product?
 
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The cross product term involves angular acceleration of the rod connecting A and B. In the Chegg problem, the angular acceleration is apparently zero.
 
How do they justify there being no angular acceleration? It doesn't say this is a static situation, so these bars should be rotating towards one another.
 
whitejac said:
How do they justify there being no angular acceleration? It doesn't say this is a static situation, so these bars should be rotating towards one another.

I figured it out. The problem states that the velocities are constant and therefore the angular accelerations are zero.
Man, reading is important. Thank you for explaining this to me!
 

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