If in the previous problem , the final `K.E.` is `3//5` of the initial `K.E.` , find the value of `e`.

Explanation

`K_(f) = (3)/(5) K_(i)` , i.e. loss is `(2)/(5) K_(i) = (2)/(5) xx (1)/(5) mu^(2)`
`Delta K = (2)/(5) xx (1)/(2) m u^(2)`
`(1)/(4) m u^(2) ( 1 - e^(2)) = (2)/(5) xx (1)/(2) m u^(2)`
`1 - e^(2) = (4)/(5)`
`e^(2) = (1)/(5)`
`e = (1)/(sqrt(5))`