Earth's escape speed at the surface is about (taking $g = 9.8$ m/s$^2$, $R = 6.4\times 10^6$ m):
A$11.2$ km/s, from $v_e = \sqrt{2gR}$
B$7.9$ km/s, equal to low-orbit speed only
C$3.0$ km/s, the lunar escape speed instead
D$30$ km/s, Earth's orbital speed around sun
Answer & Solution
Correct answer: A. $11.2$ km/s, from $v_e = \sqrt{2gR}$
$\sqrt{2\cdot 9.8\cdot 6.4\times 10^6} \approx 11200$ m/s.
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