What will be the change in phase of a wave due to reflection from a rigid support?

On producing the waves of frequency $1000 \,Hz$ in a Kundt's tube, the total distance between $6$ successive nodes is $85 \,cm$. Then, the speed of sound in the gas filled in the tube is (in $\,ms^{-1}$)

$A$ string is rigidly tied at two ends and its equation of vibration is given by $y = \sin(2\pi x) \cos(2\pi t)$. Then the minimum length of the string is .... $m$

The equation of a stationary wave is $y = 20 \sin(\pi x) \cos(\omega t)$,where $x$ and $y$ are in meters and $t$ is in seconds. The distance between a node and its adjacent antinode is (in $\text{ cm}$)

$A$ sound source of frequency $170 \, Hz$ is placed near a wall. $A$ man walking from the source towards the wall finds that there is a periodic rise and fall of sound intensity. If the speed of sound in air is $340 \, m/s$,the distance (in metres) separating the two adjacent positions of minimum intensity is

The following equations represent progressive transverse waves:
$Z_1 = A \cos(\omega t - kx)$,
$Z_2 = A \cos(\omega t + kx)$,
$Z_3 = A \cos(\omega t + ky)$,
$Z_4 = A \cos(2\omega t - 2ky)$.
$A$ stationary wave will be formed by superposing: