Rotating disc and generators

Question: A generator designed to produce very large pulses of current, consists of a large metal disc which is accelerated to rotate at high speed. A strong, uniform magnetic field is applied perpendicular to the plane of the disc.
Each radial element of the disc can be seen as a single conductor.
Calculate the magnitude of the induced e.m.f., if the radius of the disc is 2.0 m, the speed of rotation of the disc = 3000 revolutions per minute and the magnetic flux density B = 1.8 T

Answer:

The e.m.f. generated = magnetic fIux cut per second = BA per second.
Now the disc is rotating at 3000 revs per minute = 50 revs per second.

Therefore:
Area swept out by each radius per second = area of disc x number of revs per second
= pxR²x50 = px2² x 50 = 628.3 m²

Flux cut per second = e.m.f. generated = 628.3 x 1.8 = 1131 V