AIEEE 2003 Physics Solved Paper

A tuning fork of frequency 256‌Hz makes 5 beats/ second with the vibrating string of a piano.
Therefore the frequency of the vibrating string of piano is (256±5)‌Hz ie either 261‌Hz or 251‌Hz. When the tension in the piano string increases, its frequency will increases. Now since the beat frequency decreases, we can conclude that the frequency of piano string is 251‌Hz