An unstable particle is at rest and suddenly breaks up into two fragments. No external forces act on the particle or its fragments. One of the fragments has a velocity of +0.900c and a mass of 1.67 10-27 kg, while the other has a mass of 5.81 10-27 kg. What is the velocity of the more massive fragment? (Hint: This problem is similar to Example 6 in Chapter 7.)