Answers

2015-10-15T13:38:10+05:30
Humans can hear the sounds with frequency 20Hz to 20kHz. The frequency of pendulum is much lower than 20Hz. Its frequency is 0.5Hz. So we can't hear it.
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2015-10-15T16:17:33+05:30
The human ear can hear the sounds which have the frequency between 20cycles/s to 20000cycles/sec. 
The frequency of pendulum vibration is 0.5cycles/sec which is less than our range thus we cannot hear it
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