A speed reducer has 20 deg full depth teeth and consisct of a 20 tooth steel spur pinion driving a 50 tooth cast iron gear. the horse power transmitted is 12 at a pinion speed of 1200 rev/min. for a dimateral pitch of 8 teeth/ in and a face width of 1.5 in find the contact stress. the yuong's modulus of the steel is 30E6 and young's modulus of cast iron is 15E6. use a poisson's ratio of 0.3 for both materials. use equation 14-14 to calc the contact stress in the gear only.