Which of the following example represent periodic motion:
(i) A swimmer completing one (return) trip from one bank of a river to other bank,
(ii) A freely suspended bar magnet displaced from its N-S direction and released,
(iii) Haley Comet,
(iv) A hydrogen molecule rotating about its centre of mass.
(i) It is not a periodic motion. Though the motion of a swimmer is to and fro but will not have a definite period.
(ii) It is a periodic motion because a freely suspended
magnet it once displaced from N-S direction and let it go, it oscillates about its position. Hence it is S.H.M. also.
(iii) It is a periodic motion.
(iv) It is not a periodic motion.