Statics - Finding Tension

[thinkcentre12]

Homework Statement

Homework Equations

The answer in the back on the book shows 4.06i -7.61j + 5.07k. I do not understand why my signs are backwards.

The Attempt at a Solution

I ended with -4.06i +7.61j - 5.07k

 

[gneill]

The tension involved is a vector that points from B towards A. You've created a vector r_ab that points from A to B.

 

[thinkcentre12]

ok thank you. Since i did not see an arrow i was not sure which direction to pick. How did you tell?

 

[gneill]

ok thank you. Since i did not see an arrow i was not sure which direction to pick. How did you tell?

It's difficult to push with a cable :)

 

[thinkcentre12]

The tension involved is a vector that points from B towards A. You've created a vector r_ab that points from A to B.

It's difficult to push with a cable :)

That is a good point. Thank you

 

[mdrice12]

That is a good point. Thank you

Additionally, there is a weight pulling the boom downwards (or in the negative z-direction). In order to counteract this, the cable needs to pull it upwards (positive z-direction).