# Do not know where to begin

1. Sep 22, 2005

### gmuniz

Q An infinitely long line of charge has a linear charge density of 6.50*10^-12 C/m. a proton is a distance of 17.5 cm from the line and moving directly toward the line with a speed of 2900 m/s. How close does the proton get to the line charge? Im lost and do not know how to approach the problem or set it up.

2. Sep 22, 2005

### stunner5000pt

from taht distance what is the potential due to this infinite rod?
When the proton gets as close as it can all of its kinetic energy will be converted to potential energy
$$q (V_{f} - V_{i}) = \frac{1}{2} m_{p} v^2$$

Cna you find the potential at the starting point using integration? Try using variables so you cna get a general expresion. It will be useful later on.