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?

Answer 1

Answer:$v_o$

Explanation:

It is given that three cars has same mass m with speed $v_o$

suppose rest two cars also has same mass m

As there is no external force therefore momentum is conserved

Initial Momentum $P_i$

$P_i=3mv_0+m(2v_0)+m\times 0$

Final momentum $P_f$

$P_f=5m\times v$

where v=final velocity

$P_i=P_f$

$5mv_o=5mv$

$v=v_o$

thus final velocity is $v_o$