Let at time t velocity of rod be v (towards right) and current in the circuit is i (from a to b). The magnetic force on it is ilB (towards right). Writing the equation of motion of the rod.
m⋅dvdt=ilB=(E0−BlvR)lB
∫v0dvE0BlmR−B2l2mRv=∫t0dt
∴v=E0Bl⎛⎜
⎜⎝1−eB2l2mRt⎞⎟
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