Question

What is the minimum force with which each boy has to pull the rope in order to balance if each girl pulls the rope with a force of 200N
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Answer 1

Answer:

Following Newton's third law (... equal and opposite forces...), the string stretches until it reaches its tightest point.

You might imagine this to be like a tug-of-war game with both sides dead even.

Since we are focusing on horizontal forces, and since exactly two horizontal forces are pulling in opposite vector directions to the same extent, these cancel each other out, as seen here: