What gravitational force do yhe two protons in the helium nucleus exert on each other? There separation is approximately 1.0 fm.

I know that 1 fm is 10^-15 m i didn't know if that was how you figured it out to get it to N?

1 answer

To get the electrostatic force forcing the two protons apart, use Coulomb's Law

F = k e^2/r^2

where r = 10^-15 m and e is the proton (and electron) charge, in Coulomb's. The value of the constant k should be available in your notes or textbook, or can easily be found by googling "Coulomb's law"... or read
http://www.glenbrook.k12.il.us/gbssci/phys/Class/estatics/u8l3b.html

The reason the nucleus stays together is that there is an addition attractive force between bosons (protons and neutrons) called "the strong force"