Question

In the diagram below, A, B, C, D are four pendulums suspended from the same elastic string PQ. The lengths of A and C are equal to each other, while the length of pendulum B is smaller than that of D. Pendulum A is set into a mode of vibrations.

1. Name the type of vibrations taking place in pendulums B and D.
2. What is the state of pendulum C?
3. State the reason for the type of vibrations in pendulums B and C.

Answer 1

1) The vibrations which occur in pendulums B and D are called forced vibrations.

2) Pendulum C is in the state of resonance with pendulum A as it is of the same length.

3) The pendulums vibrate because the forced vibration from A is transferred due to string PQ.

Pendulum B is of a different length as compared to pendulum A. Hence, it will continuously vibrate with a frequency which is different from that of pendulum A. Its amplitude will also be very small.

Pendulum C is of the same length as compared to pendulum A. Hence, it will vibrate in phase with pendulum A. Its amplitude will be equal to that of pendulum A, as it will attain resonance.