A rifle bullet loses 1/20th of its velocity in passing through a plank. What will be the least number of such planks required to just stop the bullet? | A rifle bullet loses 1/20th of its velocity in passing through a plank. What will be the least number of such planks required to just stop the bullet is..


Let thikness is x

Initial Velocity =V

Final velocity =V{1-(1/20)}

                       =19v/20

=>(19v/20)2=v2-2ax[v2=u2-2as]

=>2as=V2[1-(19/20)2]

=>2as=V2[(39/400]-------(i)

 

For n planks

02=v2-2anx

V2=2anx-------(ii)

From equation (i)/(ii)

Therefore,

n=400/39 ≈ 10.3

So, 11planks are required to stop the bullet.


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