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NEET PHYSICSOscillationsMedium

Question

Two pendulums of length 121 cm121 \text{ cm} and 100 cm100 \text{ cm} start vibrating in phase. At some instant, the two are at their mean position in the same phase. The minimum number of vibrations of the shorter pendulum after which the two are again in phase at the mean position is:

A

8

B

11

C

9

D

10

Step-by-Step Solution

  1. Time Period Relationship: The time period (TT) of a simple pendulum is directly proportional to the square root of its length (LL): TLT \propto \sqrt{L}.
  2. Given Data: Length of longer pendulum (LLL_L) = 121 cm121 \text{ cm} Length of shorter pendulum (LSL_S) = 100 cm100 \text{ cm}
  3. Ratio of Time Periods: TLTS=LLLS=121100=1110\frac{T_L}{T_S} = \sqrt{\frac{L_L}{L_S}} = \sqrt{\frac{121}{100}} = \frac{11}{10} This implies 10TL=11TS10 T_L = 11 T_S. That is, the time taken for 10 oscillations of the longer pendulum is equal to the time taken for 11 oscillations of the shorter pendulum.
  4. Phase Condition: Two oscillating bodies starting in phase will be in phase again when the faster body (shorter pendulum) completes one more full oscillation than the slower body (longer pendulum). Let nn be the number of vibrations of the shorter pendulum. nTS=(nk)TLn T_S = (n-k) T_L For the first time they come in phase, the difference in number of oscillations is usually related to the ratio integers. From the ratio TL/TS=11/10T_L/T_S = 11/10, the smallest integers satisfying the condition nLTL=nSTSn_L T_L = n_S T_S are nL=10n_L = 10 and nS=11n_S = 11.
  5. Conclusion: The shorter pendulum completes 11 vibrations to be in phase again.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from Oscillations. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSOscillationspendulumslengthvibratinginstantposition

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