A 2070 kg railroad flatcar, which can move with negligible friction, is motionless next to a platform. A 236 kg sumo wrestler runs at 5.3 m/s along the platform (parallel to the track) and then jumps onto the flatcar.
(a) What is the speed of the flatcar if he then stands on it?
(b) What is the speed of the flatcar if he then runs at 5.3 m/s relative to it in his original direction?
(c) What is the speed of the flatcar if he then turns and runs 5.3 m/s relative to the flatcar opposite his original direction?