The pitch of the whistle of an engine appears to drop to 
of original value when it passes a stationary observer. If the speed of sound in air is 
then the speed of engine is
A
B
C
D
Text Solution
Verified by ExpertsThe correct answer is:
B
Pitch of sound depends on its frequency.
Speed of sound, 
Speed of engine, 
?
Apparent pitch (frequency) heard by observer
of original pitch (frequency) of engine.
Let original frequency of the engine be 
.
Apparent frequency heard by stationary observer 
Then 
Engine is moving away from the source
So, 
.
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