A unit mass is moved from the centre of earth to infinity, then the work done by the external force

Question

A unit mass is moved from the centre of earth to infinity, then the work done by the external force is

Professor PC Thomas Classes · Answer

The gravitational potential difference between the infinity and the center of earth is
$
V_{\infty}-V_0=-\int_0^{\infty} \vec{g} \cdot d \vec{\ell}
$