The equation of the displacement of two particles making SHM are represented by 

$y_1$ = a sin $\left(\omega t+\varphi \right)$ & $y_2$ = a cos $\left(\omega t\right)$. 

The phase difference of the velocities of the two particles is :

The motion of a particle executing simple harmonic motion is described by the displacement function, $x(t)=A\cos \left(\omega t+\varphi \right)$. 
If the initial $(t=0)$ position of the particle is 1 cm and its initial velocity is $\omega$ cm/s, what are its amplitude and initial phase angle ? The angular frequency of the particle is $\pi s^{-1}$. If instead of the cosine function we choose the sine function to describe the $SHM:x=B\sin (\omega t+\alpha )$, what are the amplitude and initial phase of the particle with the above initial conditions.