Can someone explain to me the signs on this vector problem

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To solve the vector problem involving points A and B, the correct approach is to calculate the position vector by using A-B, which ensures that the resulting force vector points away from point B, aligning with the nature of tension. The tension in cable AB is 12 kN, and the force vector on point B is derived by first finding the unit vector from A to B and then multiplying it by the tension. The discussion also touches on the electric field in a conductor, noting that it is zero due to the equilibrium of charges, despite the presence of a smaller conductor. The tension force indeed pulls away from point B, confirming that the r vector and force vector should always point in the same direction. Understanding these vector relationships is crucial for accurately solving the problem.
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Homework Statement


For drawing purposes, I'm just going to state the locations of the 2 points. Cable AB carries a tension of 12 kN. Point A=(0,0,70) m and point B=(35,-25,10) m.
Find the corresponding force on point B as a vector.




okay now this part has me confused. I'm trying to find my r vector so I can get the unit vector out of that and multiply by the tension to get the corresponding force vector.

My question is do you do B-A or A-b to get the r vector? The only way I can match the signs in the book is to do A-B, but why would it be A-B instead of B-A?
 
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can someone also answer the question why the E field in the conductor w/ the 2 radius is 0? Shouldn't there be an e field due to the smaller conductor?
 
The direction of the force on B has to point away from B. Tensions pull, they don't push. A-B points away from B. B-A doesn't.
 
oh thank you for explaining. r vector and force vector always point in same direction correct?
 
pyroknife said:
oh thank you for explaining. r vector and force vector always point in same direction correct?

I like my explanation better. Tension pulls. It should point AWAY from B.
 

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