The weight of a body on the surface of the earth is 63 N. What is the gravitational force on it due to the earth at a height equal to half the radius of the earth?

A space ship is launched into a circular orbit close to earth’s surface. What additional velocity has now to be imparted to the spaceship in the orbit to overcome the gravitational pull?

(Radius of earth = 6400 km, g = 9.8 m/s$$^2$$)

What is the maximum height attained by a body projected with a velocity equal to one-third of the escape velocity from the surface of the earth? (Radius of the earth $$=R$$ )

Two satellites $$S_1$$ and $$S_2$$ are revolving round a planet in coplanar circular orbits of radii $$r_1$$ and $$r_2$$ in the same direction, respectively. Their respective periods of revolution are $$1 \mathrm{~h}$$ and $$8 \mathrm{~h}$$. The radius of orbit of satellite $$S_1$$ is equal to $$10^4 \mathrm{~km}$$. What will be their relative speed (in $$\mathrm{km} / \mathrm{h}$$) when they are closest?