What force will be required at a radius of 8 cm to raise and lower an 11,00 kgf crossbar of a planner which is raised and lowered by two 38 mm square thread single-start screws having a pitch of 7 mm? The outside and inside diameters of the collar are 76 mm and 38 mm respectively. Assume the co-efficient of friction at the threads as 0.11 and at the collar as 0.13.