a
\(X = A \sin (\omega t +\delta)\) \(V = A \omega \cos (\omega t +\delta)\)

\(\frac{ A }{2}= A \sin (\omega t +\delta)\) \(\therefore V \text { is tve, } \delta \text { must be }\)

\(\text { At } t =0\) \(\text { in } 1^{\text {st }} \text { quadrant or } 4^{\text {th }}\)

\(\sin \delta=\frac{1}{2} \Rightarrow \delta=\frac{\pi}{6}, \frac{5 \pi}{6}\) \(\text { quadrant }\)

\(\therefore \text { Common solution is } \delta=\frac{\pi}{6}\)