$1.$ A single$-$threaded power screw is $25$ mm in diameter with a pitch of $5$ mm$.$ A vertical load onthe screw reaches a maximum of $5$ kN$.$ The coefficients of friction are $0\mathrm{.}06$ for the collar and$0\mathrm{.}09$ for the threads. The frictional diameter of the collar is $45$ mm$.$ Find the overall efficiencyand the torque to raise and lower the load.