A 15 kW and 1200 r.p.m. motor drives a compressor at 300 r.p.m. through a pair of spur gears having 20° stub teeth. The centre-to- centre distance between the shafts is 400 mm. The motor pinion is made of forged steel having an allowable static stress as 210MPa while the gear is made of cast steel having an allowable static stress as 140 MPa. Assuming that the drive operates 8 to 10 hours per day under light shock conditions, find from the standpoint of strength, (a) Module; (b) Face width and (c) Number of teeth and pitch circle diameter of each gear. Check the gears thus designed from the consideration of wear. The surface endurance limit may be taken as 700 MPa.