Why use unit vector for this, and not for that?

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Homework Help Overview

The discussion revolves around the use of unit vectors in two different physics problems, one involving a car and the other a more complex scenario requiring consideration of multiple directions. Participants are exploring why one problem employs unit vectors while the other does not.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the necessity of unit vectors in the context of the problems presented, with some noting the difference in complexity and directionality between the two scenarios. There is also a discussion about the specific application of unit vectors in calculating moments.

Discussion Status

The discussion is active, with participants providing insights into the reasoning behind the use of unit vectors in the first problem and contrasting it with the second problem. Some guidance has been offered regarding the application of unit vectors in relation to moments, but no consensus has been reached.

Contextual Notes

There is mention of the specific requirements of each problem, such as the first problem focusing on a moment about an axis and the second on a moment about a point. This distinction may influence the use of unit vectors.

viet_jon
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the car problem in my text uses the unit vector, and the second one doesn't...

how come?


zxcv.jpg


zxc-1.jpg
 
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The second problem is more complex and requires vectors to take care of the 3 directions involved. The first (car) problem has only one direction so no need for vectors.
 
but it did the opposite of just that.

the car used 'unit' vector...

while the second does not use the 'unit' vector
 
The first problem is asking for a moment about an axis. I'm pretty sure this is why you have to employ the unit vector in your calculations. If i recall correctly (been awhile since I was in statics) the unit vector here will be j or [0i 1j 0k]. Is that familiar?

The second problem is asking for a moment about a point.
 

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