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\begin{aligned} v_{\mathrm{f}} &=\sqrt{\frac{k}{m}} x_{\mathrm{i}} \\ &=\sqrt{\frac{250.0 \mathrm{~N} / \mathrm{m}}{0.100 \mathrm{~kg}}}(0.0400 \mathrm{~m}) \\ &=2.00 \mathrm{~m} / \mathrm{s} \end{aligned}