Electrostatics, finding velocity of electron

[physics604]

1. An electron orbits the nucleus of an atom with velocity v. If this electron were to orbit the same nucleus with twice the previous orbital radius, its orbital velocity would now be

a) \frac{v}{2}
b) v
c) 2v
d) \frac{v}{√2}

Homework Equations

\DeltaE_k + \DeltaE_p = 0 ?

The Attempt at a Solution

I'm not really sure how I should start this question. None of the equations I have include both the v and the r variable.

 

[berkeman]

What is the equation for electrostatic attraction?

 

[physics604]

F = kQ₁Q₂ / r²

But I don't see how that helps.

 

[berkeman]

F = kQ₁Q₂ / r²

But I don't see how that helps.

And the equation that we use for centripital force for uniform circular motion? There is a reason that we ask you to list the Relevant Equations...