Why Does Calculating Tension in Multiple Blocks Require Different Forces?

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Calculating tension in multiple blocks involves different forces due to the varying interactions between the blocks. For block A, tension can be determined using only the friction force opposing it, leading to T = Ra. However, for block B, all forces acting on it must be considered, including the tension from block A and any additional forces like friction. This difference arises because each block's equilibrium conditions depend on the forces acting on them. Understanding these dynamics is crucial for accurately calculating tension in connected systems.
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Homework Statement
Newtons 1st law, constant velocity
Relevant Equations
Sum F = 0
If I want to find the tension in the rope that connects block A and B. I can apply Newtons first law.

Sum of all forces in opposite direction equals 0.

The forces that work on block A is Friction (Ra) and the force on the rope that pulls the block towards the right (T) So we get T-Ra = 0 and therefore T=Ra. We don't look at the force T2 or mcg, or the friction working on block B.

So my question is. If we on block A only use the first force to the right and the first force to the left. (T-Ra) to find the tension in the rope connecting A and B . When we find the tension in the rope (T2) connecting B and C. Why do we have to calculate all forces that work to the left (T2 = P+Rb+Ra) instead of T2=P+Rb ?
 

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You forgot the problem statement. What is the exercise ?
 
BvU said:
You forgot the problem statement. What is the exercise ?

Nevermind. I think I got it :)
 

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