How do our ears permit us to receive sound?

What change,if any,would you expect in the characteristics of musical sound when we increase $(i)$ its frequency and (ii) its amplitude?

Give four practical uses of ultrasonic vibrations.

$A$ note is a sound:

$A$ source is producing $1500$ sound waves in $3$ seconds. If the distance covered by a compression and an adjacent rarefaction is $68 \, cm$,find $(a)$ frequency,$(b)$ wavelength,and $(c)$ velocity of the sound wave.

$(a)$ Why are sound waves called mechanical waves? List two practical applications of reflection of these waves.
$(b)$ $A$ stone is dropped from the top of a tower $125 \ m$ high into a pond of water at the base of the tower. When is the splash heard at the top? $(g = 10 \ m s^{-2}$ and speed of sound $= 340 \ m s^{-1})$