Simple harmonic motion: Pendulum

A large pendulum has 10 m10\ mlength and it has a mass of 50 kg50\ kg attached to that. The pendulum is oscillating in an under-damped condition. The initial amplitude of the oscillation is 1.2 m1.2\ mand it drops to 0.90 m0.90\ mafter 5 days. Calculate the time it takes for the total energy of this pendulum to drop by 110\frac{1}{10}factor (in days) . Include 3 decimal places in your answer.
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