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WBJEEParagraph:Two trains A and B are moving with speeds 20 m/s...
Paragraph:
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 f1=800 Hz to f2=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.Question:
The spread of frequency as observed by the passengers in train B is
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 f1=800 Hz to f2=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.Question:
The spread of frequency as observed by the passengers in train B is
Solution:
For the passengers in train B, observer is receding with velocity 30 m/s and source is approaching with velocity 20 m/s.
∴f′1=800(340−30340−20)=775 Hz and f′2=1120(340−30340−20)=1085 Hz
∴ Spread of frequency =f′2−f′1=310 Hz
∴ The correct option is (a).
∴f′1=800(340−30340−20)=775 Hz and f′2=1120(340−30340−20)=1085 Hz
∴ Spread of frequency =f′2−f′1=310 Hz
∴ The correct option is (a).
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