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

$A$ body sends waves $100 \, mm$ long through medium $A$ and $0.25 \, m$ long in medium $B$. If the velocity of waves in medium $A$ is $80 \, cm s^{-1}$,the velocity of waves in medium $B$ is .... $m s^{-1}$.

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:

The figure represents the instantaneous snapshot 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 point(s) moving downwards is/are:

The equation of a wave is given by $y = 10 \sin \left(\frac{2 \pi t}{30} + \alpha\right)$. If the displacement is $5 \ cm$ at $t = 0 \ s$,then the total phase angle at $t = 7.5 \ s$ will be:

For a wave propagating in a medium, identify the property that is independent of the others.