A comet of mass $10^8 \mathrm{kg}$ travels around the Sun in an elliptical orbit. When it is closest to the Sun it is $2.5\times 10^{11} \mathrm{m}$ away and its speed is $2\times 10^4 \mathrm{m} {\mathrm{s}}^{-1}$ . Find the change in kinetic energy when it is farthest from the Sun and is $5\times 10^{10} \mathrm{m}$ away from the Sun