Three identical train cars, coupled together, are rolling east at 2.5 m/s . A fourth car traveling east at 3.5 m/s catches up with the three and couples to make a four-car train. A moment later, the train cars hit a fifth car that was at rest on the tracks, and it couples to make a five-car train.
1. What is the speed of the five-car train? Express your answer using two significant figures.