The gravitational self potential energy of a solid ball of mass density ρ and radius R is E. What is the gravitational self potential energy of a ball of mass density ρ and radius 2R in terms of E?

It will be

E = mgh.

where h and g are constant thus

m can be written as 4/3πr^3*density

E = 4/3πr^3 * density

E? = 4/3π (2R) ^3 * density

= 4/3π8r^3

thus the e will be 4/3π8r^3 * density/4/3πr^3*density nd thus you get 8E ...