In the $xy$-plane, the region $y \gt 0$ has a uniform magnetic field ${B_1}\widehat k$ and the region $y \lt 0$ has another uniform magnetic field ${B_2}\widehat k.$ A positively charged particle is projected from the origin along the positive $y$-axis with speed ${v_0} = \pi \,m{s^{ - 1}}$ at $t=0,$ as shown in the figure. Neglect gravity in this problem. Let $t=T$ be the time when the particle crosses the $x$-axis from below for the first time. If ${B_2} = 4{B_1},$ the average speed of the particle, in $m{s^{ - 1}},$ along the $x$-axis in the time interval $T$ is $\underline{\hspace{2cm}}$.