Question

Three identical train cars, coupled together, are rolling east at speed v0. A fourth car traveling east at 2v0 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?

Express your answer in terms of v0

Answer 1

Answer:

$1v_0$

Explanation:

Assuming that cars 4 and 5 have same mass so that the momentum  

P=mv where m is mass and v is velocity hence

Momentum=0+2mv+3mv=5mv

The final mass is 2m+3m=5m

From aw of conservation of momentum

$5mv_0=5mv$ hence $v=1v_o$

Therefore, the speed is $1v_0$