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## Homework Statement

Three identical train cars, coupled together, are rolling east at 1.13 m/s. A fourth car traveling east at 6.43 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. All 5 cars are identical. What is the speed of the five-car train?

## Homework Equations

p

_{initial}= p

_{final}

m1v1+m2v2 = m

_{total}v

_{final}

## The Attempt at a Solution

so this is what i did

3mV+ mV= 4mV [the masses cancel]

(1.13)+(6.43)= V

7.56 m/s = v

4mV+ mv = 5mv

Vtotal+0 = vfinal

7.56 m/s = vfinal

can someone pls tell me what I'm doing wrong thanks