Answer:
The frequency of the piano string is 1059 Hz.
Explanation:
The frequency beat (fb), 2 beats/second, is the absolute difference between the frequency of the tuning fork (1056 Hz) and the frequency of the piano string.
As the piano string gets tightened, the frequency beat becomes 3 beats/second.
Therefore,
fb = [tex]fb = fpiano - ftuning fork\\ 3 Hz=fpiano-1056Hz\\ fpiano=1056Hz+3Hz\\ fpiano=1059Hz[/tex]