How force works on two strings connected by a mass

  • Thread starter Ezio3.1415
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  • #1
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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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  • #2
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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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  • #3
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Thank you... :)
 

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