A 35-gram stainless steel ball on a track is moving at a velocity of 9 m/s. On the same track, a 75-gram stainless steel ball is moving at a velocity of –7 m/s. After colliding, the 35-gram ball moves at a velocity of –15 m/s. Assume there is no net force on the system. What is the velocity of the 75-gram ball after the collision? Round to the nearest tenth. –4.2 m/s –0.5 m/s 0.5 m/s 4.2 m/s