Waves And Oscillations

In resonant vibrations of a body, the frequency of external force applied on the body is equal to its natural frequency. If on increasing and decreasing the frequency of external force from the natural frequency by a factor, the amplitude of vibrations reduces very much. In this case sharp resonance will take place. But if it reduces by a small factor then flat resonance will take place.
The sharp and flat resonance will depend on damping present in the body executing resonant vibrations. Less the damping, greater will he sharnness.

Let the two pendulums are in same phase, after n vibrations of the longer pendulum. In this time the shorter pendulum will complete vibrations.

By law of conservation of energy loss in PE = gain in KE At point of breaking