What is the magnitude of gravity's acceleration on the earth's surface if the radius of the earth suddenly reduces to 80% of its current value while the mass of the planet remains constant?

 

Concept:  Newton's law of gravity is referred to as "universal" since it is thought to apply to the entire Universe. It is so named because it applies to all bodies with mass (such as the sun, moon, earth, or an apple), and all bodies are governed by the same law, Newton's law of gravitation.

We can deduce the following from Newton's law of gravitation:

Since the radius is reduced to of its original value;

The new radius

Therefore;