A black hole is an object whose gravitational field is so strong that even light cannot escape from it. To what approximate radius would earth (mass $=6\times {10}^{24} \mathrm{kg}$) have to be compressed to be a black hole?

The kinetic energies of a planet in an elliptical orbit about the Sun, at positions $A, B$ and $C$ are $K_A, K_B$ and $K_C$ respectively. $AC$ is the major axis and $SB$ is perpendicular to $AB$ at the position of the Sun $S$ as shown in the figure. Then