Displacement versus time curve for a particle executing SHM is shown in the figure. Identify the points marked at which (i) velocity of the oscillator is zero, (ii) speed of the oscillator is maximum.

                               

Hint: The velocity of the oscillator is zero at the extreme position and maximum at the mean position.
Step 1: Find the positions of minimum velocity and the maximum velocity.
In SHM y-t graph, zero displacement values correspond to the mean position; where the velocity of the oscillator is maximum.
Whereas the crest and troughs represent extreme positions, where displacement is maximum and velocity of the oscillator is minimum and is zero. Hence,
1. A, C, E, G are either crest or trough having zero velocity.
2. The speed is maximum at mean positions represented by B, D, F, H points.