Question

two protons a certain distance apart exert force F in vacuum . what is the force between 2 alpha particles at same distance?

Answer 1

By Newtons law of Universal Gravitation, we have
F=\frac{GmM}{R^{2}}
Let masses of protons be m.
∴F = \frac{G{m^2}}{R^2}
Now, an alpha particle contains two protons
∴Gravitational force between them= \frac{G(2m)^2}{R^2}  
                                                           =\frac{4Gm^2}{R^2}
                                                           = 4F