Q. If an object of mass $m$ is taken from the surface of earth (radius R ) to a height 2R , then the work done is
A) $2mgR$
B) $mgR$
C) $\frac{2}{3}mgR$
D) $\frac{3}{2}mgR$
Explanation
(c) Work done
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ W = \mathrm{\Delta}U = \frac{mgh}{1 + \frac{- h}{R}}$
$Substituting\ \ R = \frac{h}{L}we\ get$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \mathrm{\Delta}U = \frac{mg \times 2R}{1 + 2}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \mathrm{\Delta}U = \frac{2mgR}{3}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.