In the railroad freight yard, an empty freight car of massm rolls along a straight level track at 1.2 m/s and collides with an initially stationary,fully loaded boxcar of mass 4.30m. The two cars couple together upon collision.

(a) What is the speed of the two cars after the collision? ___m/s (b) Suppose instead that the two cars are at rest after thecollision. With what speed was the loaded boxcar moving before thecollision if the empty one was moving at 1.20 m/s? ___m/s