$17$ A rocket is fired vertically with a speed of $5km{s}^{-1}$ from the earth's surface. How far from the earth does the rocket go before returning to the earth? Mass of the earth $=6\mathrm{.}0{10}^{31}kg$ mean radius of the earth $=6\mathrm{.}4{10}^{6}m$:$G=6\mathrm{.}67{10}^{-11}N{m}^{2}k{g}^2.$

$18.$ The escape speed of a projectile on the earth's surface is $11\mathrm{.}2km{s}^{-1}.$ A body is projected out with thrice this speed. What is the speed of the body far away from the earth? Ignore the presence of the sum and other planets.

$9$ A salellite orbits the earth at a height of $400$ km above the surface. How much energy must be expetided to rocket the satellite out of the earth's gravitational influence? Mass of the satellite $=200kg$; mass of the earth $=6\mathrm{.}0{10}^{24}kg$ : radtus of the earth $=6\mathrm{.}4{10}^{6}m$:$G=6\mathrm{.}67{10}^{-11}N{m}^{2}k{g}^{-2}.$