Does the speed of a planet remain constant in its orbit?

The mean radius of the earth's orbit around the sun is $1.5 \times 10^{11} \ m$. The mean radius of the orbit of mercury around the sun is $6 \times 10^{10} \ m$. The mercury will rotate around the sun in

The distances of two planets from the Sun are $10^{11} \ m$ and $10^{10} \ m$ respectively. Find the ratio of their orbital periods.

$A$ planet revolves around the sun whose mean distance is $1.588$ times the mean distance between the earth and the sun. The revolution time of the planet will be ........... $years$.

Explain Kepler's first law (Law of Orbits) for planetary motion.

The time period of a satellite of the Earth is $5$ hours. If the separation between the Earth and the satellite is increased to four times the previous value,the new time period will become ......... $hours$.