Two particles are performing simple
harmonic motion in a straight line about the same equilibrium point. The amplitude and time period for both particles are same and equal to
$A$ and $T$, respectively. At time
$t=0$ one particle has displacement
$A$ while the other one has displacement $\large\frac{−A}{2}$ and they are moving towards each other. If they cross each other at time t, then t is :