A quasifiliform wire whose cross-sectional area is A and whose resistivity is r is bent into a circular arc of diameter D, as shown in the figure. An additional straight length of this wire, 0P, is [ree to pivot about O and makes sliding electrical contact with the arc at P. Finally, another straight length of this wire, O), completes the circuit. The entire arrangement is located in a uniform magnetic field B directed as in the figure. The straight wire starts from rest with # = 0 rad and has a constant angular acceleration o (units of rad/s*). In terms of the given parameters, find: