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

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

c. What is the efficiency of the jack when raising the load?

d. Would the screw overhaul if a ball thrust bearing of negligible friction were used in place of the plain thrust washer?