$(a)\;\sqrt{\large\frac{2qEL}{m}} , 2qE\qquad(b)\;\sqrt{\large\frac{qEL}{m}} ,2qE \qquad(c)\;\sqrt{\large\frac{qEL}{m}} ,qE \qquad(d)\;\sqrt{\large\frac{2qEL}{m}} ,3qE $

Answer : (b) $\;\sqrt{\large\frac{qEL}{m}} ,2qE $

Explanation :

From A to B

Work done by electric field = charge in kinetic energy of particle

$l^{|}\;$ = distance travelled by particle along the direction of electric field .

$l^{|}=l-l cos 60^{0}=\large\frac{l}{2}$

Work done by electric field = $\;qEl^{|}$

$=\large\frac{qEl}{2}$

$\large\frac{qEl}{2}=\large\frac{1}{2}\;mv^2$

$v=\sqrt{\large\frac{qEl}{m}}$

At B , F .B .O of particle is

$T - qE=\large\frac{mv^2}{l}$

$T=qE+qE$

$T=2qE\;.$

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