Question

when a passenger jumps out of a moving train he falls down

Answer 1

when a passenger jumps out of a moving train he falls down because of inertia of motion

Answer 2

This is because when the passenger is sitting inside the train his body possesses inertia of motion but when he jumps out of the moving train his lower body suddenly stops but the upper body still has the inertia of motion causing him to move forward and hence the passenger falls down.
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