The largest and the shortest distance of the earth from the sun are $r_{1}$ and $r_{2}$. Its distance from the sun when it is at perpendicular to the major-axis of the orbit drawn from the sun is:

Ratio of time period of satellites orbiting around earth at a distance of about 9r and 4r from earth surface is : ( where r is the radius of earth)

কেপলারের পর্যায়কালের সূত্র —

When Johannes Kepler developed his laws (or the movement of planetary bodies), one of the law' stated that the orbits of the planets about the sun are

The mean distance of Earth from the Sun is $149.6 \times 10^6$ km and the mean distance of Mercury from the Sun is $57.9 \times10^6$ km. The period of Earth’s revolutions is 1 year, what is the period of Mercury’s revolution?