Q 11-14-090JEE MainJEE Main 2021 (26 Feb, Shift 2)Easy
A tuning fork $A$ of unknown frequency produces $5$ beats s$^{-1}$ with a fork of known frequency $340$ Hz. When fork $A$ is filed, the beat frequency decreases to $2$ beats s$^{-1}$. What is the frequency of fork $A$?
Answer: (A) $335$ Hz
Possible frequencies of $A$: $340 \pm 5 = 335$ Hz or $345$ Hz.
Filing a fork increases its frequency. For the beat frequency to fall (to $2$ Hz), the frequency must move towards $340$ Hz, so it was below $340$ Hz: $f_A = 335$ Hz (it becomes $338$ Hz after filing).
Solution by Sreeraj P, M.Sc Physics