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A whistle revolves in a circle with angu...

A whistle revolves in a circle with angular speed 0 = 20 rad/sec 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)

A

385 Hz

B

374 Hz

C

394 Hz

D

333 Hz

Text Solution

Verified by Experts

The correct Answer is:
B
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
`u. = v (V/(V+v))`
where, V and v are the velocities of sound and source respectively and v is the actual frequency. Now,
`v. = 385 xx 340/(340 + 10) = 374 Hz`
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