According to Newton's first law of motion, what happens to the ball is the ball rolls backward.
This means that an object at rest or in motion will remain uniformly rectilinear and tend to be in that state if the net force on it is zero.
In this case, we have to think that the ball is at rest and the train is moving with a velocity that way, the reaction of the ball will be to go in the opposite direction to the motion.
See more about first law at brainly.com/question/3808473
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