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  4. Two charges -Q and -9Q are placed at a separation of 3m. Where should charge q be placed so that net force on it is zero ? <img class=img-fluid question-image alt=Question src=https://cdn.tardigrade.in/q/nta/p-lai8890nwnnujzqc.jpg />

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Q. Two charges $-Q$ and $-9Q$ are placed at a separation of $3m.$ Where should charge q be placed so that net force on it is zero ?
Question

NTA AbhyasNTA Abhyas 2020

Solution:

Solution $k\frac{Q q}{x^{2}}=k\frac{q Q q}{\left(\right. 3 - x \left(\left.\right)^{2}}$
$\frac{1}{x}=\frac{3}{3 - x}$
$3-x=3x$
$4x=3$
$x=\frac{3}{4}=0.75m$