Finding Tension ACB: Problem 2.53 Solution

[CivilSigma]

For problem 2.53, they are asking us for the tension in cable ACB and the answer is 1213N.

Now to my understanding to find tension ACB, I need to find tension CB and CA then find the resultant of them, However I know that is wrong because when I calculated tension CB I got the answer of 1213N.

Now my question is, why is tension ACB = tension CB ?

Thank you in advance.
http://[Imgur](http://i.imgur.com/pOgJai9)

 

[pongo38]

If the traction cable were not there, what would happen? Is the system stable? What difference would it make if the pulley were not frictionless?