A factory horn is sounded facing a large concrete wall situated 120 m away.
a) Determine the time interval between the horn blast and the reception of its echo at an air temperature of 30 °C where the speed of sound is 349 m s⁻¹.
b) If the air temperature falls to 0 °C so that the speed of sound becomes 331 m s⁻¹, calculate the new interval and find the percentage change compared with the value obtained in part (a).