$${v = \sqrt{6,67 \cdot 10^{-11} \frac{5,972 \cdot 10^{24}\, \mathrm{kg}}{6,371\cdot 10^6\,\mathrm{m} + 400000\, \mathrm{m}}} = \underline{7,67\, \mathrm{\frac{km}{s}}}}$$