Problem $1.[5$ Marks$]$

A load of $600$ kN is to be raised and lowered by means of two square threaded

screws. If the coefficient of friction between the screw and nut is $0\mathrm{.}048,$ determine

the size of screw and nut. Take ${}_c=80$MPa,${}_b=15$MPa. Find also the torque

required to raise and lower the load. $($a$)$ First of all, it is assumed that the two

$.$screws share equal load. $($b$)$ Considering direct compressive stress in screw