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…
NEET UG 2022 — Physics Waves & Oscillations
2022mcqeasy
Two pendulums of length 121cm and 100cm 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
Official previous-year question
Held on 30 Apr 2022 · Verified 9 Jul 2026.
Options
A
9
B
10
C
8
D
11
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Solution
Time period of a pendulum,
T∝l
⇒T2T1=l2l1
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,
T2×nT1×(n−1)=1⇒100(n)121(n−1)=1
⇒11n−11=10n⇒n=11
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