Q 11-14-122JEE MainJEE Main 2019 (9 Apr, Shift 2)Easy
A string $2.0\ \text{m}$ long and fixed at its ends is driven by a $240\ \text{Hz}$ vibrator. The string vibrates in its third harmonic mode. The speed of the wave and its fundamental frequency is
Answer: (B) $320\ \text{m s}^{-1},\ 80\ \text{Hz}$
Third harmonic: $f_3 = 3f_1 = 240\ \text{Hz} \Rightarrow f_1 = 80\ \text{Hz}$.
$f_1 = \dfrac{v}{2L} \Rightarrow v = 2\times2.0\times80 = 320\ \text{m s}^{-1}$.
Solution by Sreeraj P, M.Sc Physics