Answer
(b) is true
Work Step by Step
The velocity vectors at a given point on a roller coaster will have the same direction since the track is fixed. The velocity vectors may have different lengths since the speed of each car may vary.
(a) is incorrect since the magnitudes of the velocity vectors may vary since the speed of each car may vary.
(c) is incorrect since the velocity vector at a given point will always have the same direction since the track is fixed.
