Stationary waves can be produced in

In stationary waves,the distance between a node and its nearest antinode is $20 \ cm$. The phase difference between two particles having a separation of $60 \ cm$ will be

At nodes in stationary waves,

Stationary waves are produced in a $10\,m$ long stretched string. If the string vibrates in $5$ segments and the wave velocity is $20\,m/s$,the frequency is ..... $Hz$.

$A$ wave disturbance in a medium is described by $y(x, t) = 0.02 \cos(50 \pi t + \frac{\pi}{2}) \cos(10 \pi x)$,where $x$ and $y$ are in meters and $t$ is in seconds. Which statement$(s)$ is/are correct?

$A$ standing wave is represented by $Y = A \sin(100t) \cos(0.01x)$,where $Y$ and $A$ are in millimetres,$t$ is in seconds,and $x$ is in metres. The velocity of the wave is ..... $m/s$.