Question

Q = 2V
U_i = $\frac{1}{2}\times \frac{(2V{)}^2}{2}=V^2$
$\therefore V_y = \frac{1}{2}\frac{64V^2}{25\times 8}$
$\frac{2V-q}{2}=\frac{q}{8}+\frac{1}{2}\frac{4V^2}{25\times 2}$
$\therefore$ 8V - 4q = q
U_f = $\frac{5V^2}{25}=\frac{V^2}{5}$
$\therefore q=\frac{8V}{5}$
Energy dissipated = $\frac{4V^2}{5}$

 $\therefore$  % energy
Dissipated = $\frac{4V^2}{5V^2}\times 100$ =80%