Another Electric Potential Problem

[Brit412]

Homework Statement

A charge of 2.9*10^-6C is held fixed at the origin. A second charge of 2.9*10^-6 C is released from rest at the position (1.15m, 0.550m). And the mass of the second charge is 2.10 g.
At what distance from the origin does the 2.9*10^-6 charge attain half the speed it will have at infinity?

Homework Equations

KE (final) = Potential Energy (initial) - PE (final)

The Attempt at a Solution

There was a part A to this question where I figured out the speed it had at infinity. For the second part, I tried to just solve for r using the same equation but it doesn't work. Any tips?

 

[LowlyPion]

At what distance from the origin does it start?

Now in terms of Potential Energy is concerned when the velocity is 1/2 of the final velocity, then at what radius if you released a charge would it only have 1/2 the previous part's velocity at ∞ ?

 

[Brit412]

It starts at 0,0.

 

[LowlyPion]

It starts at 0,0.

Looks to me like it is

released from rest at the position (1.15m, 0.550m)

 

[Brit412]

What should I do with that position? Should I add it to the new radius I get?

 

[LowlyPion]

What should I do with that position? Should I add it to the new radius I get?

Doesn't the initial position determine the initial potential energy?

 

[Brit412]

Yes it does...I get it now, thank you!