Question

We hear sound produced by the humming bees while that of moving pendulum is not heard.

Answer 1

pendulum makes infrasound which is not in range of human hearing (below 20Hz) whereas humming bees produce sound which is in range of normal hearing

Answer 2

the audible  human hearing range is 20Hz to 20kHz .The frequency  OF Vibration of wings of a bee is higher than 20Hz where as the vibration of pendulum is less than 20Hz there fore it is not possible for our ear to detect the sound of vibration of a pendulum on the other hand we can hear the humming of a bee