Question

the passenger move forward when train stops due to

Answer 1

Due to inertia of motion  i think that.....

Answer 2

It is due to the law of inertia. It states that a body remains at state of rest or in a uniform velocity in a straight line until n unless the external force acts on it.
Be a use of this since train was moving initially n suddenly comes to the rest the body which attained the velocity of train was still remaining though the train stopped n that velocity made the body to move forward