Question

Two identical small balls of equal charge $q$ and equal mass $m=0.9kg$ are placed at a separation of $r=1m$ in air on a rough surface. If coefficient of static friction is ${\mu }_0=0.9$. Find the magnitude of maximum charge $q$ such that both balls remain at rest:-

• A. $\pm 30\mu C$
• B. $90\mu C$
• C. $\pm 60\mu C$
• D. $+20\mu C$

Answer 1

The correct option is A $\pm 30\mu C$

$\begin{array}{c}0.9\times 0.9\times 10=\frac{k{q}^2}{1}\\ \Rightarrow \frac{9}{10}\times \frac{9}{10}\times 10=9\times {10}^9\times q^2\\ \Rightarrow q^2=9\times {10}^{-10}\\ \therefore q=3\times {10}^{-5}\\ Hence,theoptionAisthecorrectanswer.\end{array}$