Question

Car A has a siren sounding note of 540 Hz. A listener in car B hears a note of 544 Hz. Both move in the same direction. One concludes that:
(A) B leads A & moves faster
(B) B is behind & moves slower
(C) both move with the same speed.
(D) B leads A and moves slower.​

Answer 1

Given:

Car A has a siren sounding note of 540 Hz. A listener in car B hears a note of 544 Hz. Both move in the same direction.

To find:

Correct statement among the given options ?

Calculation:

This is an example of DOPPLER'S EFFECT , where the observer gets to hear an apparent frequency of a sound due to relative displacement between the observer and the source.

Now, Let's assume that car A is moving towards right ans emitting a siren with the frequency of 540 Hz ;

But , car B is listening to a sound of frequency 544 Hz :

• This is possible only when there is a relative approach between the observer and the source.

Considering the above fact, the relative approach is only possible when car B leads car A (i.e. car B is ahead of car A) and car B is driving slower.

(D) B leads A and moves slower.

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