Velocity & Acceleration in SHM question from NEET 2007 (AIPMT)

Answer: (d)

1. $x = A\sin\omega t$, $v = A\omega\cos\omega t = A\omega\sin(\omega t + \frac{\pi}{2})$.
2. $a = -A\omega^2\sin\omega t = A\omega^2\sin(\omega t + \pi)$.
3. Phase difference between $v$ and $a$ $= \pi - \frac{\pi}{2} = \frac{\pi}{2} = 0.5\pi$.
4. So the answer is (d) $0.5\pi$.