Two fixed insulating rings A and B carry ahanges with uniform linear aharge density `+lambda` and `-lambda`, respectively, as shown in the adjacent figure. The planes of the rings are parallel to each other and their axes are coinciding. A particle of change "q" and mass "m" is released with zero velocity from centre P of the positively charged ring. The kinetic energy of the particle when it reaches centre Q of the negatively charge ring will be