Question

Consider a run away train. The train has a mass of 200,000 kg. The train is traveling at 25 m/s . In an attempt to slow down the the train, the engineer puts another train in the run away train's path. The second train has a mass of 150,000kg. The second train is traveling at 15m/s in the same direction as the run away train. When the trains collide, they stick together. How fast will the train be traveling after the collision ( assume the train are not being powered by engines)