An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r. The coulomb force $\overrightarrow{F}$ between the two is :

Question

$\begin{array}{1 1} k \frac{e^2}{r^2} \hat r \\ -k \frac{e^2}{r^3} \hat r \\ k \frac{e^2}{r^3} \hat r \\ -k \frac{e^2}{r^3} \hat r \end{array} $

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How solve this question plz explain