What helped man to move around safely on land?

Assume that the earth moves around the sun in a circular orbit of radius R and there exists a planet which also moves around the sun in circular orbit with an angular speed twice as large as that of the earth. The radius of the orbit of the planet is

A satellite of mass m moves around the Earth in a circular orbit with speed v. The potential energy of the satellite is

A satellite is going in a circular orbit of radius 4 xx 10^4 km around the earth has a certain speed. (a) What will be the radius of a circular orbit of the same satellite when it moves around the planet Mars with the same speed? The masses of earth and Mars are in the ratio 10:1 and their radii are in the ratio 2:1