# Ball moving in a Train!

A ball is bouncing elastically with a speed of $$1ms^{-1}$$ between walls of a railway compartment of size $$10m$$ in a direction perpendicular to walls. The train is moving at a constant velocity of $$10ms^{-1}$$ parallel to the direction of motion of the ball. As seen from the ground

$$(A)$$ The direction of motion of the ball changes every $$10$$ seconds.

$$(B)$$ Speed of ball changes every $$10$$ seconds.

$$(C)$$ Average speed of ball over any $$20$$ second interval is fixed.

$$(D)$$ The acceleration of ball is the same when observed either from ground or train.

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