A hollow spherical shell is compressed to half its radius. The gravitational potential at the centre

Spaceman Fred's spaceship (which has negligible mass) is in an elliptical orbit about Planet Bob. The minimum distance between the spaceship and the planet is $\mathrm{R}$; the maximum distance between the spaceship and the planet is $2\mathrm{R}$. At the point of maximum distance, Spaceman Fred is traveling at speed $v_0.$ He then fires his thrusters so that he enters a circular orbit of radius $2\mathrm{R}$. What is his new speed?

Assuming potential energy '$U$' at ground level to be zero.

All objects are made up of same material:-

$U_P=$Potential energy of solid sphere

$U_Q=$Potential energy of solid cube

$U_R=$Potential energy of solid cone

$U_S=$Potential energy of solid cylinder

Two concentric shells of masses ${\mathrm{M}}_1$ and ${\mathrm{M}}_2$ are having radii ${\mathrm{r}}_1$ and ${\mathrm{r}}_2$. Which of the following given below is the right expression for the gravitational field at a distance r is