Two trains A and B are moving with speeds 20 m/s and 30 m/s, respectively in the same direction on the same straight track with B ahead of A. The engines are at the front ends. The engine of train A blows a long whistle. Assume that the sound of the whistle is composed of components varying in frequency from `f_(1)=800Hz` to `f_(2)=1120Hz`, as shown in the figure. the spread in the frequency (highest frequency-lowest frequency) is thus 320Hz. the speed of sound in still air is 340 m/s.

Q. The distribution of the sound intensity of the whistle as observed by the passengers in train A is best represented by :

Options

A.
B.
C.
D.

Answer

A

Explanation

For the passengers in train A, there is no relative motion between source and observer, as both are moving with velocity 20 m/s. Therefore, there is no change in observed frequencies and correspondingly there is no change in their intensities.