A Machine Gun Is Attached to a Railroad Flatcar That

Multiple Choice

A machine gun is attached to a railroad flatcar that rolls with negligible friction.If the railroad car has a mass of 7 × 10⁴ kg,how many bullets of mass 20 g would have to be fired at 200 m/s off the back to give the railroad car a forward velocity of 0.5 m/s?

A) 8.8
B) 0.11
C) 1,400
D) 8,750
E) ​14