Physic <span title="C.........lolz........help">C.........lolz........hel...</span> me!!!!!!!?

Question

A 2140 kg railroad flatcar, which can move with negligible friction, is motionless next to a platform. A 242 kg sumo wrestler runs at 5.3 m/s along the platform (parallel to the track) and then jumps onto the flatcar. What is the speed of the flatcar if he then (a) stands on it, (b) runs at 5.3 m/s relative to it in his original direction, and (c) turns and runs at 5.3 m/s relative to the flatcar opposite his original direction?

Answer 1

about momentum.

a) 2140(0)+242(5.3)=(2140+242)v

v=.538m/s

b) its -a, or -.538m/s

c) twice a, or 1.077m/s

make it a good day