Solving a problem in physics section 60 paragraph 96 el

96. The plane of the conducting disc homogeneous mass m = 0.4 kg is perpendicular to the direction of the magnetic field with induction B = 30 mT. In the center of the disc and its edge by means of sliding contacts is applied DC voltage. The disc starts to rotate, and after a period of time t = 40 s speed reaches ν = 10 s-1. Determine the current I, flowing through the disk.