Answer:
The frequency of the piano string is either 1053 HZ or 1059 HZ.
Step-by-step explanation:
Here we know that frequency of beats is equal to the difference between the frequencies between two waves .
Given that frequency of tuning fork is 1056 HZ .
Let the frequency of the piano be ' f ' .
Given that number of beats = 3.
We know that | 1056 - f | = 3 ;
⇒ 1056- f = ±3,
Upon solving this we get
f = 1056-3 and 1056 + 3
⇒ f = 1053 or 1059 .