A body is released from a height equal to the radius \( (R) \) of the earth. The velocity of the body when it strikes the surface of the earth will be:(Given \( g \) = acceleration due to gravity on the earth.)
\( \sqrt{\dfrac{gR}{2}} \)
\( \sqrt{4gR} \)
\( \sqrt{gR} \)
\( \sqrt{2gR} \)