Two smooth spheres of masses 4 kg and 2 kg impinge obliquely. The 2 kg mass is brought to rest by the impact. (i) Prove that, before impact, they were moving in directions perpendicular to each other. (ii) Show that, as a result of impact, the kinetic energy gained by the 4 kg mass is equal to half that lost by the 2 kg mass. I'm having trouble proving the first part because to prove it i'd need to show that e = 1/2 however no value of e is given. Is this possible to solve or is the information incomplete?