1. Feb 4, 2015 #1

   thinkcentre12

   

   1. The problem statement, all variables and given/known data
   
   
   
   2. Relevant 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.
   
   
   3. The attempt at a solution
   
   
   
   I ended with -4.06i +7.61j - 5.07k

    

   thinkcentre12, Feb 4, 2015
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3. Feb 4, 2015 #2

   gneill

   

   Staff: Mentor

   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.

    

   gneill, Feb 4, 2015
4. Feb 4, 2015 #3

   thinkcentre12

   

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

    

   thinkcentre12, Feb 4, 2015
5. Feb 4, 2015 #4

   gneill

   

   Staff: Mentor

   It's difficult to push with a cable :)

    

   gneill, Feb 4, 2015
6. Feb 4, 2015 #5

   thinkcentre12

   

   
   That is a good point. Thank you

    

   thinkcentre12, Feb 4, 2015
7. Feb 4, 2015 #6

   mdrice12

   

   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).

    

   mdrice12, Feb 4, 2015

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