A screw jack has square threads with a mean radius 38 mm and pitch of 15 mm. Consider m = 0.06. If the lever is of length 0.4 m find the force that has to be applied at the end of the lever to lift up...

A screw jack has square threads with a mean radius 38 mm and pitch of 15 mm. Consider m = 0.06. If the lever is of length 0.4 m find the force that has to be applied at the end of the lever to lift up a load of 8 kN. Is the screw jack self locking? If not, find the force required at the end of the lever to prevent the load from descending.