Two planets revolve around the sun with frequencies ${N_1}$ and ${N_2}$ revolutions per year. If their average orbital radii are ${R_1}$ and ${R_2}$ respectively,then ${R_1}/{R_2}$ is equal to:

$A$ planet orbits in an elliptical path of eccentricity $e$ around a massive star considered fixed at one of the foci. The point in space,where it is closest to the star is denoted by $P$ and the point,where it is farthest is denoted by $A$. Let $v_P$ and $v_A$ be the respective speeds at $P$ and $A$,then

$A$ satellite moves in a circle around the earth. The radius of this circle is equal to one half of the radius of the moon's orbit. The satellite completes one revolution in

The period of a satellite in a circular orbit of radius $R$ is $T$. The period of another satellite in a circular orbit of radius $4R$ is:

$A$ 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 ........... $years$.

The Earth revolves around the Sun in one year. If the distance between them becomes double,the new period of revolution will be