A double threaded Acme stub screw of 2-inch major diameter is used in a jack having a plain thrust collar of 2.5

inch mean diameter. Coefficients of running friction are estimated as 0.10 for the collar and 0.11 for the screw.

(a) Determine the pitch, lead, thread depth, mean pitch diameter, and helix angle of the screw.

(b) Estimate the starting torque for raising and for lowering a 5000 lb load.

(c) If the screw is lifting a 5000 lb load at the rate of 4 ft/min, what is the screw rpm? What is the efficiency of the jack under this steady-state condition?

(d)Would the screw overhaul if a ball thrust bearing (of negligible friction) were used in place of the plain thrust collar.