State three conditions necessary for sound to be heard.

Define frequency,amplitude,and speed of a sound wave.

State whether the following statement is true or false: Sound waves travel faster in air than in water.

The audible range for a normal human being is

$(a)$ $A$ particular transmitter of Aakashvani broadcasts at $420.5\, m$ wavelength. Given the speed of radio waves $3 \times 10^{8}\, m s^{-1}$. Calculate the frequency at which the radio station broadcasts its programme.
$(b)$ What is the direction of oscillations of the medium particles through which a
$(i)$ transverse wave is propagating?
$(ii)$ longitudinal wave is propagating?

$(a)$ 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 $= 340 \ m s^{-1})$