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[tex]\large\boxed{\begin{array}{l}\rm" a~forc_{\!\!,}a~de~atrac_{\!\!,}\tilde ao~ou~de~repuls\tilde ao~entre~duas\\\rm cargas~\acute eletricas~puntiformes~\acute e~diretamente\\\rm proporcional~ao~produto~das~cargas\\\rm e~inversamente~proporcional~ao~quadrado\\\rm da~dist\hat ancia~que~as~separa.\\\underline{\tt matematicamente:}\\\huge\boxed{\boxed{\boxed{\boxed{\sf F=\dfrac{k\cdot q_1\cdot q_2}{d^2}}}}}\end{array}}[/tex]
[tex]\large\boxed{\begin{array}{l}\bf dados:\\\sf q_1=q_2=Q\\\sf d=3~m\\\sf F=40~N\\\sf k=9\cdot10^9\\\sf F=\dfrac{k\cdot q_1\cdot q_2}{d^2}\\\sf 40=\dfrac{9\cdot10^9\cdot Q^2}{3^2}\\\sf40=\dfrac{\diagdown\!\!\!9\cdot10^9\cdot Q^2}{\diagdown\!\!\!9}\\\sf Q^2=\dfrac{40}{10^9}\\\sf Q^2=\dfrac{4\cdot10}{10^9}\\\sf Q^2=4\cdot10^{1-9}\\\sf Q^2=4\cdot10^{-8}\\\sf Q=\sqrt{4\cdot10^{-8}}\\\sf Q=2\cdot10^{-4}C\\\huge\boxed{\boxed{\boxed{\boxed{\sf\maltese~alternativa~c}}}}\end{array}}[/tex]
