How Is Electric Potential Energy Calculated in Electron Orbit Problems?

[Destrio]

Homework Statement

An electron orbits a nucleus which carries a charge of +9.6E-19 C. If the electron's orbit radius is 2.0E-10 m, what is its electric potential energy?

Homework Equations

Ep = kQ1Q2/r
V = kQ/r
V = Ep/Q

The Attempt at a Solution

I tried using Ep = kQ1Q2/r
Ep = (9E9)(9.6E-19C)(-1.6E-19C) / (2.0E-10m)
Ep = -6.9E-18 J
the answer key is saying -6.9E-19 J

and V = kQ/r , V = Ep/Q
V = (9E9)(9.6E-19C) / (2.0E-10m)
V = 43.2 V
V = Ep/Q
Ep = 43.2 V x (1.6E-19)
Ep = -6.9E-18 J
the answer key is saying -6.9E-19 J

Am I doing something wrong, or is the answer key off by an exponent?

Thanks,

 

[marlon]

you seem to be very correct to me

marlon

 

[Destrio]

ok, thank you