An elementary particle of mass $m$ and charge $+e$ is projected with velocity $v$ at a much more massive particle of charge $Ze$,where $Z > 0$. What is the closest possible approach of the incident particle?

• A
  $\frac{Ze^2}{2\pi \varepsilon_0 mv^2}$
• B
  $\frac{Ze}{4\pi \varepsilon_0 mv^2}$
• C
  $\frac{Ze^2}{8\pi \varepsilon_0 mv^2}$
• D
  $\frac{Ze}{8\pi \varepsilon_0 mv^2}$