# Electron travel in a wire; distance

1. Oct 20, 2009

### megr_ftw

1. The problem statement, all variables and given/known data
The starter motor of a car engine draws a current of 140 A from the battery. The copper wire to the motor is 5.0 mm in diameter and 1.2 m long. The starter motor runs for 0.95 s until the car engine starts.

How far does an electron travel along the wire while the starter motor is on?

2. Relevant equations
drift velocity= (j) / (en)
j= current density, e=elementary charge, n=concentration of gases in material(given in book)

j= I/A

3. The attempt at a solution
I found the charge that passes through the starter motor to be 133 Coulombs. Am I suppose to incorporate the equation for drift velocity in order to find the distance?

2. Oct 20, 2009

### megr_ftw

and I actually just found the current density to be 7130141.45 A/m^2 using the second equation.
now, how am I suppose to go from this to the distance the electron travels after 0.95 seconds??

3. Nov 15, 2010

### physeven

you can use simple mechanics. consider the electron a point charge moving with a uniform drift velocity and i presume you will get the solution. just don't expect me to get it for you though.