a bullet emerges out from a wooden plank wit 75%of its initial kinetic energy. the number of additional planks required to stop the bullet is? (ans: 3) 

Dear Student,

Please find below the solution to the asked query:

Here, Given that the bullet emerges from the plank with 75% of its initial kinetic energy. So,

12mV2=34×12mU2  V = 32U
Let the thickness of the plank is t. So, the acceleration offered by the plank is,

V2-U2=2as  a=32U2-U22t a=-U28t
If n number of planks are needed to stop the bullet. Then,

V'2-U2=2ant  02-U2=2-U28t nt  -U2=-n U24 n=4
So, 3 additional planks are required to stop the bullet.


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