The orbital speed of Jupiter is

The distance between the centre of the Earth and the Moon is $384000 \, km$. If the mass of the Earth is $6 \times 10^{24} \, kg$ and $G = 6.67 \times 10^{-11} \, N m^2/kg^2$,the orbital speed of the Moon is nearly ......... $km/s$.

The orbital velocity of an Earth satellite near the surface is $7 \, km/s$. When the radius of the orbit is $4$ times the radius of the Earth,the orbital velocity in that orbit is ......... $km/s$.

Which one of the following statements is correct?

$A$ planet of mass $m$ is moving around a star of mass $M$ and radius $R$ in a circular orbit of radius $r$. The star abruptly shrinks to half its radius without any loss of mass. What change will be there in the orbit of the planet?

Earth is moving around the sun in an elliptical orbit as shown. The ratio of $OB$ and $OA$ is $R$. Then the ratio of Earth's velocities at $A$ and $B$ is