Question

A spacecraft is in orbit at an altitude of 100 km above the surface of the moon.

What is its speed? Mmoon = 7.34 x 1022 kg and Rmoon = 1.84 x 106 m

Answer 1

$$v=\sqrt{G\frac{M}{r}}\\ =\sqrt{6.67*10^{-11}*\frac{7.34*10^{22}}{1.84*10^6+100*10^3}}=1589\:\rm m/s$$