$\begin{array}{1 1}\sqrt{40}ms^{-1}\\\sqrt{30}ms^{-1}\\\sqrt{15}ms^{-1}\\\sqrt{13}ms^{-1}\end{array} $

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Answer : $\sqrt{40}ms^{-1}$

The work done by the resistance is $6\times 3 =18J\qquad$ Decreases K.E so negative

The work done by the force is $\int\limits_{2^5} \large\frac{40}{x^2}$$dx$

$\Rightarrow \big[\large\frac{-40}{x}\big]_2^5$$=12J\qquad$ Increases K.E so positive

Final K.E = Initial K.E-work done by resistance + work done by force

$\Rightarrow \large\frac{1}{2}$$\times 0.5V^2=\large\frac{1}{2}$$\times 0.5\times 8^2-18+12=10J$

$\Rightarrow V=\sqrt{40}ms^{-1}$

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