$A$ progressive sound wave is represented by $y = a \sin(400\pi t - \pi x / 6.85)$,where $x$ is in $m$ and $t$ is in $s$. The frequency of the wave is .... $Hz$.

The figure represents the instantaneous picture of a longitudinal harmonic wave travelling along the negative $x$-axis. Identify the correct statement$(s)$ related to the movement of the points shown in the figure. The stationary points are

Which of the following functions for $y$ can never represent a travelling wave?

The equation of a longitudinal wave is represented as $y = 20 \cos \pi (50t - x)$. Its wavelength is ..... $cm$.

The figure represents the instantaneous picture of a transverse harmonic wave travelling along the negative $x$-axis. Identify the correct statement(s) related to the movement of the points shown in the figure. The points moving opposite to the direction of propagation (i.e., moving in the negative $y$-direction) are:

$A$ simple harmonic progressive wave is represented by $y = A \sin(120\pi t + 3x)$. The distance between two points on the wave at a phase difference of $\frac{\pi}{3} \text{ radian}$ is