Calculating Electric Potential for a Wire with Linear Charge Density?

[mjolnir80]

Homework Statement

the wire in the image below has a linear charge density $$\lambda$$ . what is the electric potential at the center of the semicircle?
http://img18.imageshack.us/img18/5139/physicsproblem.jpg

Homework Equations

The Attempt at a Solution

i know that the potential from the semi circle is V=KQ/R
but I am having a little trouble figuring out how to calculate the potential from the other 2R pieces of wire.
can someone help me out here :)

 

[rl.bhat]

Consider a small element dx at a distance x from the center P on either 2R piece. Charge on this piece is lambda*dx. Potential due to this piece dV = K*lambda*dx/( R + x ). To find the potential due one piece find the integration between the limits x = R to x = (2R + R). Then double it to get the total potential due to two straight pieces.

 

[mjolnir80]

Consider a small element dx at a distance x from the center P on either 2R piece. Charge on this piece is lambda*dx. Potential due to this piece dV = K*lambda*dx/( R + x ). To find the potential due one piece find the integration between the limits x = R to x = (2R + R). Then double it to get the total potential due to two straight pieces.

thanks allot for the help