Olaf is standing on a sheet of ice that covers the football stadium parking lot in buffalo, new york; there is negligible friction between his feet and the ice. a friend throws olaf a ball of mass 0.400 kg that is traveling horizontally at 10.8 m/s . olaf's mass is 65.9 kg . if the ball hits olaf and bounces off his chest horizontally at 7.50 m/s in the opposite direction, what is his speed vf after the collision?