c
Using energy conservation

\(KE _{ i }+ PE _{ i }= KE _{ f }+ PE _{ f }\)

\(O +\frac{2 KP }{ a ^{3}} \times P =\frac{1}{2} mv ^{2} \times 2+0\)

\(V =\sqrt{\frac{2 P ^{2}}{4 \pi \varepsilon_{0} a ^{3} m }}=\frac{ P }{ a } \sqrt{\frac{1}{2 \pi \varepsilon_{0} am }}\)