A nucleus is at rest in the laboratory frame of reference. Show that if it disintegrates into two smaller nuclei the products must move in opposite directions.

Explanation

Let mass of nucelus is m and initial velocity v=0 by law of conservation of linear momentum
`vecp_(i)=vec_(f)`
`0=m_(1)v_(1)+m_(2)vecv_(2)`
`therefore vec v_(2)=(m_(1))/(m_(2)).vecv_(1)`
negative sign shows that velocity of both fragment are in mutually opposoite direction