1. The problem statement, all variables and given/known data Q1. What's the reason behind two identical objects interchanging their velocities upon head-on collision? Why cant just each individual particles just reverse its direction and keep travelling at its original speed? Kinetic energies and momentum would still be conserved. Q2. Why can't we use the formula of Kinetic energy where kinetic energy is half mass times velocity squared to find kinetic energies of objects whose mass is changing? Is there a way to modify the formula to get the desired output?