Question

If the mass of a planet is 3.80 1024 kg, and its radius is 2.20 106 m, what is the magnitude of the gravitational field, g, on the planet's surface?

Answer 1

F = m g = G m M /r^2

g = G M/r^2

where
G = 6.67 * 10^-11
M = 3.80 * 10^24
r = 2.20 * 10^6

Answer 2

A moving electron passes near the nucleus of a gold atom, which contains 79 protons and 118 neutrons. At a particular moment the electron is a distance of 4.5 × 10−9 m from the gold nucleus.