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Two of the three tuning forks have known frequencies. When a 610 Hz fork and the unknown fork are struck together, four beats per second are heard. When a 605 Hz fork is struck with the unknown fork, beats are produced that are too numerous to count accurately. What is the frequency of the unknown fork?


614


606

Verified Answer :

AL2006


-- In combination with 610 Hz, the beat frequency is 4 Hz.

So the unknown frequency is either (610+4) = 614 Hz
or else (610-4) = 606 Hz.

In combination with 605 Hz, the beat frequency will be
either (614-605) = 9 Hz or else (606-605) = 1 Hz.

-- In actuality, when combined with the 605 Hz, the beat
frequency is too high to count accurately.  That must be
the 9 Hz rather than the 1 Hz.

So the unknown is (605+9) = 614 Hz.
 

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