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

The displacement of a particle in a medium is $y = 10^{-4} \sin(100t + 20x + \frac{\pi}{3}) \ m$,where $t$ is in seconds and $x$ is in metres. The speed of the wave is (in $m/s$)

$A$ sound wave of frequency $500 \text{ Hz}$ travels between two points $X$ and $Y$ separated by a distance of $600 \text{ m}$ in a time of $2 \text{ s}$. The number of waves between the points $X$ and $Y$ are

In the wave equation $y = 0.5 \sin \frac{2 \pi}{\lambda}(400 t - x ) \, m$,the velocity of the wave will be ......... $m/s$.

$A$ wave is given by $Y = 3 \sin 2 \pi \left( \frac{t}{0.04} - \frac{x}{0.01} \right)$ where $Y$ is in $cm$. The frequency of the wave and the maximum acceleration will be $(\pi^2 = 10)$.

The figure shows a sinusoidal wave at a given instant. Which points are in the same phase?