Question

A bullet losses 1/n of its velocity in passing through a plank. What is the least number of plancks required to stop the bullet ? (Assuming constant retardation)

Answer 1

By using `v^(2) =u^(2) + 2as`
We have `(u- (u)/(n))^(2) =u^(2) + 2(-a)s`
`rArr ((2)/(n) - (1)/(n^(2)))u^(2) = 2as`
Let no. of placks required be N
Then,
` 0^(2) =u^(2) + 2(-a)Ns`
Therefore , `((2)/(n) - (1)/(n^(2)))u^(2) = (u^(2))/(N)`
`rArr N = (n^(2))/(2n-1)`