Calculate the gravitational force between a proton and an electron separated by a distance of ${10}^{-10}\mathrm{m}$.$\left(\mathrm{G}=6.67\times {10}^{-11}{\mathrm{m}}^3{\mathrm{kg}}^{-1}{\mathrm{s}}^{-2}\right)$

A mass $\mathrm{m}$ is placed at the centre of a thin, hollow, spherical shell of mass $\mathrm{M}$ and radius $\mathrm{r}$ shown in the diagram $\mathrm{a}$. Determine the gravitational force the mass experiences.

A mass $\mathrm{m}$ is placed at the centre of a thin, hollow, spherical shell of mass $\mathrm{M}$ and radius $\mathrm{r}$ shown in the diagram $\mathrm{a}$. Determine the gravitational force the mass $\mathrm{m}$ exerts on $\mathrm{M}$

A mass $\mathrm{m}$ is placed at the centre of a thin, hollow, spherical shell of mass $\mathrm{M}$ and radius $\mathrm{r}$ shown in the diagram. 

A second mass $\mathrm{m}$ is now placed a distance of $2\mathrm{r}$ from the centre of the shell, as shown in the diagram $b$, determine the gravitational force the mass inside the shell experience. 

A mass $\mathrm{m}$ is placed at the centre of a thin, hollow, spherical shell of mass $\mathrm{M}$ and radius $\mathrm{r}$ shown in the diagram $\mathrm{a}$. 

A second mass $\mathrm{m}$ is now placed a distance or $2\mathrm{r}$ from the centre of the shell, as shown in the diagram $b$,Suggest what gravitational force is experienced by the mass outside the shell
 

Stars $\mathrm{A}$ and $\mathrm{B}$ have the same mass and the radius of the star $\mathrm{A}$is nine times larger than the radius of star $\mathrm{B}$. Calculate the ration of the gravitational field strength on star $\mathrm{A}$ to that on $\mathrm{B}$

A star explodes and loses half its mass. Its radius becomes half as large. Determine the new gravitational field strength on the surface of the star in terms of the original one