\({V_{sphere}} = \frac{{ - GM}}{{2{R^3}}}\left[ {3{R^2} - {{\left( {\frac{R}{2}} \right)}^2}} \right]\)
\( = \frac{{ - GM}}{{2{R^3}}}\left( {\frac{{11{R^2}}}{4}} \right) = - 11\frac{{GM}}{{8R}}\)
Due to cavity part potential at point \(P\)
\({V_{cavity}} = - \frac{3}{2}\frac{{\frac{{GM}}{8}}}{{\frac{R}{2}}} = - \frac{{3GM}}{{8R}}\)
So potential at the center of carvity
\( = {V_{sphere}} - {V_{cavity}} = - \frac{{11GM}}{{8R}} - \left( { - \frac{3}{8}\frac{{GM}}{R}} \right)\)
\( = \frac{{ - GM}}{R}\)
કારણ : વિષુવવૃત્ત પર ગુરુત્વપ્રવેગનું મૂલ્ય સૌથી ઓછું હોય.