Kim is tuning a piano. She strikes a 440 Hz tuning fork and a string at the same time and hears 4 beats per second.

Question

a) What are the possibe frequencies of the string?

b)She tightens the string a little then repeats. She now hears 1 beat per second. What is the frequency of the string?

Answer 1

444, 436 will give a beat of 4

She tightens it, so F goes up. so it must be 439 , and she started low at 436

Answer 2

but I do wonder how she heard 4 beats/sec, then 1beat/second. That is well below the lowest frequency humans can perceive.