Gravity and the Moon

Is g really constant?

The moon orbits the earth at a mean distance of 3.82e5 km with an orbital period of 27.3 days. It has a mass of 7.36e22.

Answer the following questions:

• What is the force needed to keep the moon in orbit around the earth?
• Is this force = mg?

Other useful information:

• Mass of earth = 5.98e24 kg
• Radius of Earth = 6.37e3 km
• G = 6.67e-11 N m^2 / kg ^2