Question

# In Fig. 7.15, A, B, C and D are the four pendulums suspended from the same elastic string XY. The lengths of pendulum A and D are equal, while the length of pendulum B is shorter and of the pendulum C is longer. The pendulum A  is set into vibrations.  (a) What is your observation about the virbations of pendulum D ? (b) Give reason for your observation in part (a). (c) What type of vibrations take place in pendulums B and C ? (d) Give reason for the answer in part (c) .

Solution

## (i) Pendulum D IS in a  state of  resonance . (ii)D HAS same length as that of A so its natural time period is same that of A so both remain in same phase hence resonance takes place (iii) forced vibrations takes place. (iv) since the length of B AND C are different as of A so thier amplitudes will be different also their time period hence resonance condition not satisfied . hence forced vibrations

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