hi gabriel,

 

It is a misconception that the ball is not moving.Think about it.....the train is moving....so are you....the ball is in your hand.If the ball wer not moving with you, would it not be left behind???

But since you see the ball to be at rest....or the velocity of the ball relative 2 you is 0, the ball must be moving with the same velocity(vector) as you.This velocity is retained when you throw the ball up as there is no force in the horizontal direction.

The ball when thrown upwards has two velocities.

1. vertical due to throwing upwards

2. horizontal due to the motion of the train.

 

If the velocity of the train is constant then the ball falls into the hand. Because the train and the ball have equal horizotal velocities.

 

If the train accelerates the ball will fall behind and if retards it will fall in front of the person.

 

Once the ball leaves the hand it is under gravity.

 

For the person who throws the ball it is in verticla motion.

But for a person on the platform the ball is in parabolic motion.