Q. A charged particle $q$ is shot towards another charged particle $\mathcal{Q}$ which is fixed, with a speed$\ v$. It approaches$\mathcal{Q}$ upto a closest distance $r$ and then returns. If $q$ is shot with speed2$v$, the closest distance of approach would be

A) $\frac{r}{4}$
B) $\frac{r}{2}$
C) $2r$
D) $r$
Explanation

(a) $\frac{1}{2}\ mv^{2} = \frac{k\mathcal{Q}q}{r_{1}}$
$\frac{1}{2}m\left( 4v^{2} \right) = \frac{k\mathcal{Q}q}{r_{2}}$
From Eqs.(i) and ($ii$), we get
$\frac{r_{1}}{r_{2}}$ =4
$r_{2} = \frac{r}{4}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.