How do I calculate the potential energy (v) between a stationary electron and a helium nucleus 800 pm apart?

Answer 1

E=(k q1 q2)/r

in this equation k is a constant equal to 9.0*10^9 N m2 C-2
q1 and q2 are the charges of the two particles you are considering (for an electron it is e(electron charge)=1.60*10^-19C, for an alpha particle (that is a helium nucleus) it should be 2e).
r is the distance between the two particles. Remember to use meters!!

hope it helps=)