Give reasons for the following:
$(a)$ The reverberation time of a hall used for speeches should be very short.
$(b)$ $A$ vibrating body produces sound. However,no sound is heard when a simple pendulum oscillates in air.
$(c)$ Sounds of same loudness and pitch but produced by different musical instruments like a violin and flute are distinguishable.

(N/A) The reverberation time of a hall used for speeches should be very short so that the speech remains clear and intelligible. If the reverberation time is long,the reflected sound waves overlap with the original sound,causing confusion and making it difficult to understand the words.
$(b)$ For a sound to be audible to the human ear,it must have a frequency between $20 \, Hz$ and $20,000 \, Hz$. $A$ simple pendulum oscillates at a very low frequency (much less than $20 \, Hz$),which is in the infrasonic range and therefore cannot be heard by humans.
$(c)$ Sounds of the same loudness and pitch can be distinguished due to the 'quality' or 'timbre' of the sound. This is determined by the waveform or the presence of overtones produced by the specific instrument,which makes each instrument's sound unique.