Q5.17 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.
Let the mass of parent nuclei be m.
And the mass of daughter nuclei be m1 and m2.
Initial momentum is zero since the nuclei is at rest.
But after dissociation, the momentum becomes :
Using conservation of momentum,
or
Thus both velocities have opposite direction.