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

If mass of an atom is M and it is moving with speed v, what be its spe

1.	If mass of an atom is M and it is moving with speed v, what be its speed after the emission of an alpha - particle if speed of alpha - particle is zero ?
Answer» `(MV)/(M+2)` `(Mv)/(M-4)` `(Mv)/(M+4)` `(M-4)/(Mv)` ANSWER :B