A) \[2mg\,R\]
B) \[mg\text{ }R\]
C) \[-mg\text{ }R\]
D) zero
Correct Answer: A
Solution :
The potential energy of the body on the surface of earth \[={{U}_{1}}=\frac{GMm}{R}\]. The potential energy of the body at infinity \[{{U}_{2}}=0\] \[\Delta U={{U}_{2}}-{{U}_{1}}\] \[=\frac{GMm}{R}=mg\,\,R\] \[\left( \therefore \,\,g=\frac{Gm}{{{R}^{2}}} \right)\] Hence, energy required = mgR
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