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Q13.1: NCERT Physics - Part 2 OSCILLATIONS 13.1 Solution: Which of the following examples represent periodic motion? (a)…
⚠️ Common Exam Traps & Conceptual Pitfalls
Students often mistake any repetitive motion for periodic motion; however, periodicity strictly requires the motion to repeat at equal intervals of time, meaning the swimmer's trip is not periodic because the time taken for each return is not constant.
Which of the following examples represent periodic motion? (a) A swimmer completing one (return) trip from one bank of a river to the other and back. (b) A freely suspended bar magnet displaced from its N-S direction and released. (c) A hydrogen molecule rotating about its centre of mass. (d) An arrow released from a bow.
Step-by-Step Verified Solution
**Answer:** (b) and (c) represent periodic motion.
**Step-by-Step Explanation:**
(a) The swimmer's motion is not periodic because there is no definite time period for the return trip.
(b) A freely suspended bar magnet displaced from its N-S direction and released executes periodic motion. It oscillates about its equilibrium position with a definite period [citation:13].
(c) When a hydrogen molecule rotates about its centre of mass, it comes to the same position again and again after equal intervals of time. Hence, it is periodic motion [citation:10].
(d) An arrow released from a bow moves only in the forward direction. It does not come back, so it is not periodic motion [citation:13].
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