a bullet flying hirizontally can pierce 9 blocks of same thickness losing 75% of its total kinetic energy. the additonal number of blocks required to just arrest the bullet is:

4 years ago

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Dear Ram Sai Charan,


Ans:- Let the initial velocity is U the final velocity is V Then from the given relation we have V²=0.75U²


or V=√3/2U


Let the retardation for each block is =f


then V²=U² - 2f(9x)


where x=thickness of each plate


So U²/4=18fx


Let the total no of block required to stop it from it's initial velocity is n


Then U²=2fnx


or   72fx=2fnx


or   n=36


Hence the excess no of plates required=36-9=27(ans) 


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Soumyajit Das IIT Kharagpur

4 years ago

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