Question

A person, pressing his ear on the railway tracks can hear an approaching train. This is possible due to:
A) Vibration of railway tracks.
B) Vibration of air
C) More speed of sound in solid medium
D) Hearing ability of the man

Answer 1

To solve this question, we should focus on the concept of speed of sound. Sound travels at different speeds in different objects. The speed of sound is maximum in solid. Sound travels most slowly in gas. We can easily see the difference in speed in our day to day life. we can use the same theory to find the correct answer to this question.

Complete step by step answer:
We know that sound is a kind of vibration. This vibration will generate in various forms and spectra. The train produces a lot of vibration. the vibration so produced can be transmitted by two mediums i.e, the air around the train and the tracks. We know more transmission will occur if more particles or molecules are present. Air has less number of molecules per volume than that of tracks. So more and better transmission of sound will occur through train tracks. We can say Metals or irons are excellent conductors of vibrational energy.
So, in tracks, the sound of the train is at a higher decibel level that can be heard at a very long distance.
And hence we can hear the sound easily by putting your ear on the track because the loudness of the sound is higher than that of the vibration of the wheel.

So therefore option (C) is correct.

Note: The sound wave travels very fast in solid. Its speed is $5100$ $m{s^{ - 1}}$ which is around 15 times the speed of sound in air. This is mostly because of the placement of molecules. air has fewer molecules per unit volume whereas metals or here iron has more molecules per unit volume. This makes transmission easier.