physics
posted by amber .
Suppose a single electron orbits about a nucleus containing two protons (+2e), as would be the case for a helium atom from which one of the two naturally occurring electrons is removed. The radius of the orbit is 2.65 1011 m. Determine the magnitude of the electron's centripetal acceleration.

V^2/R is the centripetal acceleration. You know the value of R. You can get the velocity V by setting the centripetal force equal to the Coulomb force:
m V^2/R = k Q^2/R^2
In this case, Q = 2e
k is the Coulomb constant.
m is the electron mass and e is its charge.
You will need to look up these numbers. 
do it yourself :)