Chapter 15, Problem 26A

To determine

To Explain: The effect on the times for runners if the timing started when sound was heard.

Answer to Problem 26A

Runners will get less time for race when the sound of piston is used.

Explanation of Solution

Introduction:

Sound is a mechanical wave which requires medium for its propagation. It is a longitudinal wave in which the direction of the displacement of particle is in the same or opposite to the direction in which wave propagates.

Light is electromagnetic wave. It does not require medium for its propagation. It is a transverse wave in which the direction of displacement of particle is in perpendicular to the direction in which the wave propagates.

The speed of light is greater than the speed of sound.

The approximate speed of sound in air is $0.3$ m/s whereas the speed of light is $3\times {10}^8$ m/s.

If the running time start when the sound was heard instead of sight from starter’s pistol then runners will get less time for $100\text{ m}$ .

The time taken by light to reach at the officials at the finish line will be negligible as compared as compared to time take by sound from piston.

Therefore, runners will get less time for race when the sound of piston is used.