Three identical train cars, coupled together are rolling east at 2.0 m/s. A fourth car traveling east at 4.0 m/s catches up with the three and couples to make a fourcar 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. What is the speed of the five car train?

The value is  

Explanation:

From the question we are told that

   The velocity of the each of the three cars is

    The velocity of the fourth car is  

    The initial velocity of the fifth car

Generally from the law of momentum conservation we have that

Given that the cars are identical then their mass will be the same

i.e

=>  

=>  

= >  

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