Explanation

(b) Electric force (F) is straight forwarded, given by
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ F = qE$
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Where, q is charge and E is electric field.
Given, $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ q = 3e$
$\therefore$ F=3e$E\ \ \ \ \ \ \ $…(i)
From Newton’s law, force experienced by a particle of mass 2m witn acceleration $a$ is
$F = 2ma\ldots.(ii)\ $
Equating Eqs. (i) and (ii) we get
$3eE = 2ma$
$\Rightarrow \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ a = \frac{3eE}{2m}$