If mass of an atom is M moving with speed v, what will be its speed after the emission of an `alpha`-particle if speed of `alpha`-particle is zero ?

Options

A. `(Mv)/(M+2)`
B. `(Mv)/(M-4)`
C. `(Mv)/(M+4)`
D. `(M-4)/(Mv)`

Answer

B

Explanation

Applying the prinicple of momemtum conservation,
`Mv=(M-4)v' " "[because ` the speed of the `alpha`-particles is zero`]`
`implies v'=(Mv)/(M-4)`