Shell it out

Classical Mechanics Level 2

A green sphere of mass $m_b$ is placed inside a spherical shell of radius $R$ and mass $M_s$ . Two spheres identical in mass to the green sphere are placed a distance $d$ to the right and to the bottom, respectively, of it. What is the magnitude of the gravitational force on the green sphere?

\sqrt{2}\frac{Gm_b^2}{d^2}

大概{2}\ \压裂{Gm_b ^ 2} {d ^ 2} + \压裂{Gm_bM_s} {R ^2}

2\frac{Gm_b^2}{d^2} + \frac{Gm_bM_s}{R^2}

2\frac{Gm_b^2}{d^2}