A string 2.0 m long and fixed at its ends is driven by a 270 Hz vibrator. The string vibrates in its third harmonic mode. The speed of the wave (in m/s), is (Answer the nearest integer)

Frequency of vibration of a string in nth harmonic is given by  $f_n=n.\frac{v}{2l}$ ……… (i)
Where , V= speed of sound and 
  $l$ = length of string
Here, $f_3=270Hz,$  $l$ =2 m  and n=3
Substituting these values in eq(i) we get
 $$\begin{gathered} \therefore 270=3\times \frac{v}{2\times 2} \\ \Rightarrow v=\frac{4\times 270}{3}=360m{s}^{-1} \end{gathered}$$