In the hand press shown in the cross$-$section below, a book tightening process is carried out using a load of F$-400$ kg$.$ The screw shaft used in the press is a square screw and h$=3$mm and d$=24$mm$.$ The friction coefficient on the screw thread surface is $0\mathrm{.}15.$ The mandatory stress of the screw shaft material is given as $40$MPa. The real $3$D view close to the appearance of the press is given on the side. Accordingly;

a$)$ Find the stress occurring in the screw shaft

b$)$ Find the force that must be applied to the press arm with an arm length of $600$mm so that F$=400$ kg

c$)$ Show whether the screw shaft is safe under these working condition

square section vida