A) 35
B) 30
C) 25
D) 21
Correct Answer: D
Solution :
Key Idea: Pendulum having greater time period makes one oscillation less than the other. Since, both the pendulums will be in same phase after some time, hence pendulum having greater time period \[({{T}_{2}}=2.1\,s)\] makes one oscillation less than the other \[({{T}_{2}}=2\,s)\]. Time taken by pendulum A to make n oscillations is 2 n Time taken by pendulum \[B=2.1\,(n-1)\] Hence, \[2\,n=2.1\,(n-1)\] \[\Rightarrow \] \[n=\frac{2.1}{0.1}=21\]You need to login to perform this action.
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