The radius of the moons approximately circular orbit is

Question

The radius of the Moon's approximately circular orbit is 384,000 km and its period is 27.3 days. Estimate the mass of the Earth.

[G = 6.67 × 10^-11 N m² kg^-2.]

The actual mass is 5.97 × 10²⁴ kg. What is the main reason for the error in your estimate?

An artificial satellite is to be placed in a circular orbit around the Earth so as to be 'geostationary'. What must the radius of its orbit be?

[The period of the Earth's rotation is 23 h 56 m, not 24 h. Why?]