A connector `AB` can slide without frictiion along a `II`-shaped conductor located in a horizontal plane (Fig). The connector has a length `l`, mass `m` and resistance `R`. The whole system is located in a unifrom magnetic field of induction `B` directed vertically. At the moment `t = 0` a constant horizontal force `F` starts acting on the connector shifting it translationwise to the right. Find how th e velocity o fhte connector varies with time `t`. The inductance of the loop and the resistance of the II-shaped conductor conductor are assumed to be negligible