A sinusoidal wave `y=a sin ((2pi)/lambda x-omegat)` is travelling on a stretched string. An observer is travelling along positive x direction with a velocity equal to that of the wave. Find the angle that the velocity of a particle on the string at `x=lambda/6` makes with `-x` direction as seen by the observer at time `t=0`.

Answer

`theta=tan^(-1)((api)/lambda)`