A hammer is struck against a steel railway line at station A. A guard at station B keeps one ear on the rail and the other ear open to the air. The straight-line distance between the two stations is 4.0km. The guard hears the sound through the rail 4.0s before he hears it through the air. Take the speed of sound in air as 340ms−1.
(i) Calculate the time taken by the sound to reach the guard through air.
(ii) Hence find the time taken by the sound to reach the guard through the steel rail.
(iii) Determine the speed of sound in the steel rail.
(iv) State one reason, based on particle arrangement, for the difference between the two speeds obtained.