Answer:
the initial frequency is 445Hz
Explanation:
The number of beat produce is equal to the difference in frequencies
The expression for frequency beat is
is the final frequency
is the initial frequency
The expression frequency in term of length is
where,
f is the frequency
v is the speed
L is the length
From the above ,it is clear that frequency is directly proportional to length,
after the length of the trumpet increase , the frequency produced by it decrease , since the beat frequency increases. If the initial frequency is 435Hz , the frequency produced by the trumpet is less than the value of 5beat/sec
Hence, there is no chance to produce 3 beat/sec when it sound is 440Hz ,
that means the number of beat produced should be greater than 5beat/sec.
If the initial frequency is 445Hz , the frequency produced b the trumpet is less than value of 445Hz. Thus , there will be a chance to produce 3beat/sec when it turn into tuning fork of 440Hz
Therefore, the initial frequency is 445Hz