a railroad car with a mass of 90,000 kg is traveling along a straight, horizontal track at a constant speed of 2 m/s. the car collides with a second railroad car, also with a of 90,000 kg that is initially at rest. The railroad cars stick together after the collision, as shown in the figure.

1) 0.5 m/s
2) 1 m/s
3) 2 m/s
​