Question

Two pendulums have time periods t and 5T/4. They start SHM at the same time from the
mean position. After how many oscillations of the smaller pendulum they will be again in
the same phase
(A) 5
(B) 4
(C) 11
(D) 9​

Answer 1

The bigger pendulum will complete its oscillation in time 1.25 T. In this time, the bigger pendulum will cover a phase of 2π.

The smaller pendulum will cover a phase of 1.25 * 2π = 2.5π in this time, using phasor diagram.

Hence, phase difference = 2.5π - 2π= 0.5π

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