Calculate velocity in a "simple electric train"

[raymondd]

Homework Statement

How do you calculate the velocity of the battery with 2 magnets attached on polar ends moving in a coiled copper wire

Relevant Equations

unknown

How do you calculate the terminal velocity of the train moving in a coiled copper wire with two magnets attached to the polar ends?
I have attached someone else's work I've found on the internet here and need help

 

[malawi_glenn]

What are your own thought and attempts?