Past exam of the mathematics course of the University of Cambridge / 2016 / ib / Paper 3 / 17D / b / ii / Solution

The Lorentz force on the current-carrying bar isThere is no friction force along the rails. The battery part accelerates the bar rightward for positive ${\mathcal{E}}_0{B}_0$, whereas the induced-current part is the opposing force $-B_0^2{L}^2\dot{s}/R$.