Q119 / 200 · NEET 2022 (Phase 1) · Physics

Two pendulums of length 121 cm and 100 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
    9
  • B
    10
  • C
    8
  • Correct answer
    D
    11

Solution

Time period of a pendulum,

T∝l

⇒T1T2=l1l2

If n is the number of vibrations after which the pendulums are again in phase, the number of vibration of the longer pendulum will be n-1. Therefore,

T1×n-1T2×n=1 ⇒121n-1100n=1

⇒11n-11=10n ⇒n=11

Hence, the correct answer is option: 'D'.

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