JEE Advanced 2018 Paper 1

In the xy-plane, the region y>0 has a uniform magnetic field B1

−

k

and the region y<0 has another uniform magnetic field B2

−

k

A positively charged particle is projected from the origin along the positive y-axis with speed v0=πm/s 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 B2=4B1, the average speed of the particle, in

m

s

, along x - axis in the time interval T is________________.