Question

1. if there is no external force on the object is given zero velocity? explain.
2. two objects of different mass moving in a parabolic trajectory. how the magnitude of the force of gravity and gravitational acceleration experienced by the two objects on the same trajectory?
3. why do we fall forward when the train is moving slowed / braked to a stop and fall backward when the train speeded / sped from rest?
4. why distance when the train stops at a distance farther than when the truck stops?