NEET UG 2004 — Waves & Oscillations

Which one of the following statements is true for the speed $v$ and the acceleration $a$ of particle executing simple harmonic motion?

The phase difference between two waves represented by $\begin{aligned} & y_1=10^{-6} \sin [100 t+(x / 50)+0.5] \mathrm{m} \\ & y_1=10^{-6} \cos [100 t+(x / 50)] \mathrm{m} \end{aligned}$ where $x$ is expressed in metres and $t$ is expressed in seconds is approximately