A tunnel is dug along a diameter of earth of mass M_e and radius R_e . Force on a particle of mass 'm' placed in the tunnel at a distance 'r' from the centre is :

• A

  $\frac{{\mathrm{GM}}_{\mathrm{e}}\mathrm{m}}{{\mathrm{R}}_{\mathrm{e}}^3}\mathrm{r}$

• B

  $\frac{{\mathrm{GM}}_{\mathrm{e}}\mathrm{m}}{{\mathrm{R}}_{\mathrm{e}}^3\mathrm{r}}$

• C

  $\frac{{\mathrm{GM}}_{\mathrm{e}}{\mathrm{mR}}_{\mathrm{e}}^3}{\mathrm{r}}$

• D

  $\frac{{\mathrm{GM}}_{\mathrm{e}}\mathrm{m}}{{\mathrm{R}}_{\mathrm{e}}^2}\mathrm{r}$