A charge particle 'q' is shot towards another charged particle 'Q' which is fixed , with a speed 'v'.It approaches 'Q' upto a closest distance r and then returns . If q were given a speed of '2v' the closest distance of approach would be

Question

$(a)\;\large\frac{r}{2}\qquad(b)\;2r\qquad(c)\;r\qquad(d)\;\large\frac{r}{4}$