Chapter 30 - Nuclear Reactions and Elementary Particles - Learning Path Questions and Exercises - Conceptual Questions - Page 1029: 1

When both particles are moving towards each other, the magnitude of the total momentum is only the difference between the magnitudes of their individual momenta. As per the conservation of momentum, the total momentum after collision will be less than if one were at rest. In turn, the particles have less kinetic energies, so the reaction requires less incident kinetic energy.

When both particles are moving towards each other, the magnitude of the total momentum is only the difference between the magnitudes of their individual momenta. As per the conservation of momentum, the total momentum after collision will be less than if one were at rest. In turn, the particles have less kinetic energies, so the reaction requires less incident kinetic energy.