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**1. Homework Statement**

Three identical train cars, coupled together, are rolling east at 3.97 m/s. A fourth car travelling east at 4.59 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. What is the speed of the five-car train?

**2. Homework Equations**

p=mv

Momentum is conserved

**3. The Attempt at a Solution**

Given- V(1,2,3)= 3.97 m/s

v(initial of 4)= 4.59

Find- v(1,2,3,4,5)

p at the instant 4 hits 1,2,3

p at the instant 5 hits 1,2,3,4

Cart 4- P=mv

P= 4.59m (initially)

Cart 1,2,3

P=mv

P=3m(3.97)=11.91m

When 4 collides with 1,2,3

p(of 4)=p(of 1,2,3)

4.59m=11.91m

Change in momentum=11.91m-4.59m=7.32m

When 1,2,3,4 collides with 5

P(1,2,3,4)=7.32m

P(1,2,3,4,5)=7.32m-mv

Really stuck after this. ..is anything i did above incorrect?:grumpy:

any help will be appreciated greatly :!!)

**1. Homework Statement**

**2. Homework Equations**

**3. The Attempt at a Solution**