A uniform circular disc has radius `R` and mass `m`. A particle, also of mass `m`, if fixed at a point A on the edge of the disc as shown in the figure. The disc can rotate freely about a horizontal chord PQ that is at a distance `R//4` from the centre `C` of the disc. The line AC is perpendicular to `PQ`. Initially the disc is held vertical with the point A at its highest position. it is then allowed to fall, so that it starts rotation about PQ. Find the linear speed of the particle as it reaches its lowest position.