Question

A charge $q={10}^{-6}C$ of mass $2g$ is free to move when released at a distance ${}^{\prime }{a}^{\prime }$ from the fixed charge $Q$.
Calculate its speed, when it moves to a distance $b$
[Assume $a=1\text{m}$,$b=10\text{m},Q={10}^{-3}\text{C}]$

• A. $90\text{m/s}$
• B. $9\text{m/s}$.
• C. $900\text{m/s}$.
• D. None of these

Answer 1

The correct option is A $90\text{m/s}$

By work energy theorem
$W=\Delta KE\Rightarrow -\frac{KQq}{b}+\frac{KQq}{a}=\frac{1}{2}m{v}^2$
$v=\sqrt{\frac{2KQq}{m}\left[\frac{-a+b}{ab}\right]}$
$v=\sqrt{\frac{2\times 9\times {10}^9\times {10}^{-3}\times {10}^{-6}}{2\times {10}^{-3}}\left[\frac{10-1}{10}\right]}$
$v=90\text{m/s}$