Chapter 25, Problem 47A

(a)

To determine

To identify: Whether frequency observed by the person increase, decrease or stay the same.

Answer to Problem 47A

When a whistle shrieks from a railroad locomotive, starting from rest, moving towards the observer, then frequency received increases.

Explanation of Solution

Introduction:

Frequency is inversely proportional to the wavelength $\lambda$ and related to the speed of sound v as

  $v=f\times \lambda$

When a railroad locomotive starting from rest moves towards the observer, then whistle shrieks along with it. As the distance between the source and observer decreases, the frequency of the sound in air increases.

Conclusion:

When a whistle blows from a railroad locomotive starting from rest, moving towards the observer, then frequency increases.

(b)

To determine

To identify: Whether frequency observed by the person increase, decrease or stay the same.

Answer to Problem 47A

When a whistle shrieks from a railroad locomotive, starting from rest, moving towards the observer, then wavelength received decreases.

Explanation of Solution

Introduction:

Frequency is inversely proportional to the wavelength $\lambda$ and related to the speed of sound v as

  $v=f\times \lambda$

When a railroad locomotive starting from rest moves towards the observer, then whistle shrieks along with it. As the distance between the source and observer decreases, the frequency of the sound in air increases and wavelength of the sound waves decrease.

Conclusion:

When a whistle blows from a railroad locomotive starting from rest, moving towards the observer, then frequency increases and wavelength decreases.

(c)

To determine

To identify: Whether the speed of sound observed by the person changes or not.

Answer to Problem 47A

When a whistle shrieks from a railroad locomotive, starting from rest, moving towards the observer, then the speed of sound in the air in between remain constant.

Explanation of Solution

Introduction:

Frequency is inversely proportional to the wavelength $\lambda$ and related to the speed of sound v as

  $v=f\times \lambda$

Here, the speed of sound waves in the air remains constant. As it does not depends on any of such factors like frequency or wavelength of the sound waves. While frequency increases, wavelength decreases, maintaining the constant speed of the sound in the air.

Conclusion:

When a whistle blows from a railroad locomotive, starting from rest, moving towards the observer, then the speed of sound in the air in between remain constant.