$A$ person fires a gun standing at a distance of $55 \, m$ from a wall. If the speed of sound is $330 \, m s^{-1}$,find the time taken for an echo to be heard. (in $s$)

$(a)$ Mention two practical applications of reflection of sound waves.
$(b)$ How is the pressure variation in a sound wave amplified in the human ear?
$(c)$ In a ripple tank,$10$ ripples are produced per second. If the distance between a trough and a neighbouring crest is $12 \, cm$,calculate the frequency,wavelength,and velocity of the wave.

Answer the following:
$(i)$ Can transverse waves travel in gases?
$(ii)$ Can longitudinal waves travel in solid,liquid as well as gas?
$(iii)$ At any instant,a compression is formed at a point. After how much time $(a)$ a rarefaction $(b)$ a compression will be formed at the same point?

Hertz is a unit of

Given that sound travels in air at $340 \, m s^{-1}$,find the wavelength of the waves in air produced by a $20 \, Hz$ sound source. If the same source is put in a water tank,what would be the wavelength of the sound waves in water? (Given,speed of the sound in water $= 1480 \, m s^{-1}$)

$A$ person fires a gun in front of a building $167 \ m$ away. If the speed of sound is $334 \ m \ s^{-1}$,calculate the time in which he hears an echo. (in $s$)