Chapter 15.1, Problem 10SSC

To determine

To Explain: Themethod of putting ear to a railway track to get an early warning of an approaching train.

Explanation of Solution

Introduction:

In different kinds of medium, sound travels with different speed.

For propagation,sound needs a medium. The speed of sound in a medium depends upon its densityandelasticity.

As per density and elasticity of medium, sound’s speed is largest in solids, lesser in liquids and least in gases.

The railways tracks are made of iron (solid).

Speed of sound in iron is faster( $5130{\text{ m/s at 25}}^{\text{o}}\text{C}$ ) than in air ( ${\text{343 m/s at 20}}^{\text{o}}\text{C}$ ),thus first the soundwhich travelled in iron rail can be heard and then, the sound which travelled in air can be heard. Therefore, putting the ear to the track can provide early warning of the approaching train.

Conclusion:

Thus, because sound travels faster in iron than in air, putting the ear to the railway track provides an early warning of the approaching train.