$\frac{\mathrm{k} \mathrm{Q}^{2}}{2 \mathrm{R}_{0}}+\mathrm{O}=\frac{\mathrm{k} \mathrm{Q}^{2}}{2 \mathrm{R}}+\frac{1}{2} \mathrm{mv}^{2}$
$V=\sqrt{\frac{k Q^{2}}{m}\left(\frac{1}{R_{0}}-\frac{1}{R}\right)}$
$1.$ A sphere $2.$ Cylindrical
$3.$ Pear $4.$ Lightning conductor
are mounted on insulating stands and charged. The one which is best suited to retain the charges for a longer time is



