When a wave propagating in one medium enters another medium,which of the following characteristics remains constant?

The figure represents the instantaneous picture of a transverse harmonic wave traveling along the negative $x$-axis. Choose the correct alternative(s) related to the movement of the points shown in the figure. The points moving with maximum velocity is/are:

Define wave speed.

The transverse displacement $y(x, t)$ of a wave on a string is given by $y(x, t) = e^{-(ax^2 + bt^2 + 2\sqrt{ab}xt)}$. This represents a:

Two waves are represented by the equations $y_1 = A \sin (\omega t + kx + 0.57) \ m$ and $y_2 = A \cos (\omega t + kx) \ m$,where $x$ is in metre and $t$ is in second. What is the phase difference between them?

The diagram below shows the propagation of a wave. Which points are in the same phase?