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QAIPM-2002-Ph-2809: NEET 2002 Physics - Class 11 AIPM-2002-Ph-2809 Solution: A whistle revolves in a circle with angular speed \( =20\…
A whistle revolves in a circle with angular speed using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer which is far away from the centre (velocity of sound = 340 m/s)
Multiple Choice Options
- A 385 Hz
- B 374 Hz
- C 394 Hz
- D 333 Hz.
Step-by-Step Verified Solution
The whistle is revolving in a circle of radius 50 cm. So the source (whistle) is moving and the observer is fixed.
The minimum frequency will be heard by the observer when the linear velocity of the whistle (source) will be in a direction as shown in the figure, i.e. when the source is receding.
The apparent frequency heard by the observer is then
given by _ _ = _ ( v V + v )
where V and v are the velocities of sound and source respectively and _ is the actual frequency.
Now v = r _ = 0.5 _ 20 = 10 m / s
V = 340 m/s, _ = 385 Hz.
_ _ _ = 385 _ 340 340 + 10 = 374 Hz