Earthquakes produce which kind of sound before the main shock wave begins?

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.

What do you understand by the term sound energy?

$(a)$ Write two points of difference between sound wave and light wave.
$(b)$ Write an expression relating wave velocity, wavelength and frequency if speed of sound in air is $340 \, m s^{-1}$.
Calculate:
$(i)$ Wavelength when frequency $= 256 \, Hz$.
$(ii)$ Frequency when wavelength $= 0.85 \, m$.

What is an echo? When can we distinctly hear the echo of a sharp sound? Why cannot we hear an echo in small halls?

State three factors on which the speed of sound in a medium depends.