velocity of a bar on parallel conducting rails

1. The problem statement, all variables and given/known data

A pair of parallel conducting rails a distance l apart in a uniform magnetic field B⃗ . A resistance R is connected across the rails. The bar has mass m and is initially at rest. A constant force F⃗ e to the right is applied to the bar. Find its velocity as a function of time in terms of R. l, B, m, Fe, and t

2. Relevant equations

F=ma

3. The attempt at a solution

First part of the question asked to formulate Newton’s second law for the bar, and my answer was m(dv/dt) = Fe – (B^2*l^2*v)/R.

This is correct, but trying to get v(t), i move Fe to one side, everything else to the other, then factor v out (not sure if that is allowed…) and then divide the Fe by what is left. I get:

(Fe*R*t)/(m*R+B^2*l^2*t)

Any help would be greatly appreciated, thanks.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

http://ift.tt/1gak1Nl

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