• # question_answer If a body is to be projected vertically upwards from the earths surface to reach a height of 10R from the surface of the earth (where R is the radius of earth). The velocity required to do so is: A)  $\sqrt{\frac{24}{11}g\,\,R}$                B)  $\sqrt{\frac{22}{11}g\,\,R}$C)  $\sqrt{\frac{20}{11}g\,\,R}$    D)  $\sqrt{\frac{18}{11}g\,\,R}$

By the law of conservation of energy $\frac{GMm}{R}+\frac{1}{2}m{{V}^{2}}=\frac{GMm}{10R+R}+0$ $V=\sqrt{\frac{20}{11}\left( \frac{Gm}{R} \right)}=\sqrt{\frac{20}{11}}gR$