The speed of sound of the whistle is [2007]

Question

Two trains A and B 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 $f_{1}$ = 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. [2007]

Q. The speed of sound of the whistle is

Smart Achievers · Accepted Answer

(2)

The speed of sound depends on the frame of reference of the observer.

$V_{S A} = 340 + 20 = 360 m/s$

and $V_{S B} = 340 - 30 = 310 m/s$

Solution

1 340 m/s for passengers in A and 310 m/s for passengers in B

2 360 m/s for passengers in A and 310 m/s for passengers in B

3 310 m/s for passengers in A and 360 m/s for passengers in B

4 340 m/s for passengers in both the trains.

Ans.
(2)

The speed of sound depends on the frame of reference of the observer.

$V_{S A} = 340 + 20 = 360 m/s$

and $V_{S B} = 340 - 30 = 310 m/s$

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