# How fast is the rod moving after it has traveled 8.00 m down the rails?

1. Oct 21, 2009

### sweetipie2216

1. The problem statement, all variables and given/known data
An electromagnetic rail gun can fire a projectile using a magnetic field and an electric current. Consider two parallel conducting rails, separated by 0.530 m, which run north and south. A 49.0 g conducting rod is placed across the tracks and a battery is connected between the tracks, with its positive terminal connected to the east track. A magnetic field of magnitude 0.750 T is directed perpendicular to the plane of the rails and rod. A current of 2.00 A passes through the rod.
If there is no friction between the rails and the rod, how fast is the rod moving after it has traveled 8.00 m down the rails?

2. Relevant equations

a=(IL(([mu0(I))/(2\pi*r)))/m

3. The attempt at a solution

(2(.530)(4pi-7(2))/(2pi(.53))/.049 = 1.63e-5
sqrt{2*1.63e-5*8}=.016

this answer is wrong. can you please tell me what i am doing wrong and help me out?Thanks.

2. Oct 21, 2009

### Delphi51

Sweet, I don't recognize that formula! Can you derive it from basic formulas for us? I would expect you to use Fm = I*L*B in this problem - the formula for the magnetic field causing a force on a current.

3. Oct 21, 2009

### sweetipie2216

i got the answer, thanks for trying to help

4. Oct 21, 2009

### Delphi51

Sorry, I'm still not with you. I see you are using F = ma but why not
F =ILB? Where does the mu and pi come from? I would begin with
F = ma
ILB = ma