In stationary waves,antinodes are the points where there is

The speed of a stationary wave represented by the equation $y = 0.7 \sin \left(\frac{7 \pi}{4} x\right) \cos (350 \pi t)$ is (In the given equation $x$ and $y$ are in metre and $t$ is in second). (in $m \ s^{-1}$)

The equation of a stationary wave is $y = 0.8 \cos \left( \frac{\pi x}{20} \right) \sin (200 \pi t)$,where $x$ is in $cm$ and $t$ is in $sec$. The separation between consecutive nodes will be .... $cm$.

Which two of the given transverse waves will produce stationary waves when superimposed?
${z_1} = a\cos(kx - \omega t)$.....$(A)$
${z_2} = a\cos(kx + \omega t)$.....$(B)$
${z_3} = a\cos(ky - \omega t)$.....$(C)$

The given diagram shows a detector placed between a transmitter of sound waves and a metal plate. At three adjacent points,$R, S$ and $T$,the meter shows zero intensity. Which of the following is the frequency of the emitted wave in $Hz$? (Take the velocity of sound as $v = 300 \, m/s$)

In stationary waves,