1. The problem statement, all variables and given/known data In frame S , particle 1 is at rest and particle 2 is moving to the right with velocity v. Consider frame S ′ , moving relative to S , with speed u. Find the value of u such that the two particles appear in S ′ to be approaching each other with equal but opposite velocities. I don't see here how you can get the particles to approach each other. 1. The problem statement, all variables and given/known data Calculate the range of speeds for a particle of mass m in which the classical relation for kinetic energy is within 1% of the correct relativistic value. For this can I use K/T = 0.01 and solve for the velocity of the mass, where K is newtonian KE and T is relativistic KE?