2 There are two jack screw assemblies both with an ISO Metric Trapezoidal 'Tr 16 x 3' screw, one single-thread and the other double-thread. Each assembly raises and then lowers a load of 450 kg. A ball-thrust bearing forms part of each assembly and therefore collar friction is negligible. The coefficient of sliding friction for both screws is 0.08. (a) For each assembly, determine: (1) (ii) (iii) Which assembly is the most efficient in lifting? One way of ensuring that a lifting device can be made to self-lock is to use a thrust collar rather than a ball-thrust bearing. For any of the assemblies found to be back-driveable in (a)(iii), what is the minimum collar diameter required to ensure it/they would self-lock? (Assume the same value of friction coefficient of 0.08 in all situations). (b) (c) the pitch, pitch diameter, lead and lead angle; the running torque required to lower the load; whether they are back-driveable or self-locking?