21. Michael and his twin brother have a combined mass of 225 kg and are zooming along in a 45 kg amusement park bumper car at 12 m/s. They bump into Sarah's car, which is at rest. Sarah has a mass of 35 kg. After they collide, the twins continue ahead with a speed of 2.5 m/s. How fast is Sarah's car bumped across the floor?
