A string $2.0\, m$ long and fixed at its end is driven by a $240\, Hz$ vibrator. The string vibrates in its third harmonic mode. The speed of the wave and its fundamental frequency is
JEE MAIN 2019, Medium
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We have:
$f=\frac{n v}{2 \ell}$
$240=\frac{3 \times v}{2 \times 2}$
$\Rightarrow \quad v=320 \mathrm{m} / \mathrm{s}$
Fundamental frequency $=\frac{v}{2 \ell}=80 \mathrm{Hz}$
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