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Two trains A and B moving with speeds 20...

Two trains `A and B` moving with speeds `20m//s` and `30m//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) = 800 Hz` to `f_(2) = 1120 Hz`, as shown in the figure. the spread in the frequency (highest frequency - lowest frequency) is thus `320 Hz`. the speed of sound in still air is `340 m//s`.
(5) The distribution of the sound intensity of the whistle as observed by the passengers in train `A` is best represented by

A

B

C

D

Text Solution

Verified by Experts

The correct Answer is:
A
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. Therefore, the correct option is `(a)`.
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