An object is allowed to fall from a height $R$ above the earth, where $R$ is the radius of earth. Its velocity when it strikes the earth's surface, ignoring air resistance, will be :

If a satellite orbits as close to the earth's surface as possible,

Two satellites of earth $S_1$ and $S_2$ are moving in the same orbit. The mass of $S_1$ is four times the mass of $S_2$. Which one of the following statement is true ?

A satellite of mass m is at a distance of $'a'$ from a star of mass $M.$ The speed of the satellite is $u.$ Suppose the law of universal gravity is $F=-G\frac{Mm}{r^{2.1}}$ instead of $F=-G\frac{Mm}{r^{2}}$ find the speed of the satellite when it is at $a$ distance $b$ from the star.