A ball is thrown upward in the air by a passenger on a train that is moving with constant velocity. (a) Describe the path of the ball as seen by the passenger. Describe the path as seen by a stationary observer outside the train. (b) How would these observations change if the train were accelerating along the track?

When train moves with constant velocity,
(a) Then path observed by the man in train will be the straight line, where as path observed by the man at the ground will be parabolic. 
when train is accelerating then man in the train will observe the path as the parabolic whereas outside man will also observe the ball as parabolic.