# Relativistic mechanics (qualitative)

## Homework Statement

1) suppose nucleus A collides with nucleus B. A nuclear reaction takes place, producing nucleus C and nucleus D. why is it that the minimum energy required for this reaction to take place is when the reaction products both have zero momentum in the center-of-mass frame?

2) is momentum conserved in a nuclear reaction?

## The Attempt at a Solution

1) I dun see why they must have zero momentum in the center-of-mass frame. Because if they have zero momentum in the center-of-mass frame, that would mean that their velocity is zero in the center-of-mass frame, which would also mean that in the laboratory frame, they would have some velocity. wouldn't it be better if they have zero momentum in the laboratory frame?

2) normally, we say that momentum is conserved in the system if there's no net external forces that act on the system. In a nuclear reaction, there's no net external force that acts on the system of particles, but since there is change in the internal energy of the system(particles), would that result in non-conservation of momentum?

thanks