How force works on two strings connected by a mass

AI Thread Summary
When pulling two strings connected by a mass, the tension in each string behaves differently based on the speed of the pull. If the A string is pulled slowly, the B string experiences a greater tension due to the additional weight, causing it to break first. Conversely, if the A string is pulled suddenly, the acceleration increases significantly, resulting in the tension in the A string surpassing that of the B string, which remains intact. This behavior can be explained using Newton's second law, where the net force changes based on the rate of acceleration. Understanding these dynamics is crucial for analyzing the forces at play in such systems.
Ezio3.1415
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So if I slowly pull the A string first B string will tear apart... Cause the A string will expand and it will pull the mass and B string... So B string will reach its breaking weight before A... Cause B has an additional weight mg working on it..

But if I suddenly pull the A string,it will tear apart but the B string will remain intact... I am trying to understand why this happens... I mean what is the exact mechanism here?
 

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Applying Newton's second law to the block we have

Fnet = ma
FA - FB + mg = ma
FA - FB = m(a-g).

If you pull it slowly, acceleration a is negligible and we get

FA - FB = -mg < 0
FA < FB

FB is larger.

But if you pull very fast than a is very large and we get

FA - FB = m(a-g) >0

FA > FB

FA is larger.
 
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Thank you... :)
 

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