Verified answer

given the information provided: "never".

i.e. without some idea of what amount of friction to assume (i.e. coefficient of kinetic friction), there's no way to predict how long it will travel before stopping....

the retarding force Fdrag = mu * N, where N is the normal force (weight) of 50000kg*9.8m/s^2, and mu is this coefficient of kinetic friction.

the Fdrag results in a deceleration given by a=Fdrag/m. so, if you had mu, you copuld calculate Fdrag, then using that deceleration (a) you could calculate the distance the train travels until vf=0.

vf^2 = vi^2 + 2*a*s

and

vf=0

vi=9m/s

a=Fdrag/m = mu*g (negative number)

then solve for s in meters...

cheers