break the steps down simply, I am very confused. An unstable particle is at rest and suddenly decays into two fragments. No external forces act on the particle or its fragments. One of the fragments has a speed of 0.53c and a mass of 6.68 * 10 ^ - 27 * kg while the other has a mass of 1.67 * 10 ^ - 27 * kg 1) What's the speed of the less massive fragment