$(3)$ If cable $AB$ is subjected to a tension of $500$ N $,$ determine the tension in cables $AC$

and $AD$ and the magnitude of the vertical force $F.$

$(4)$ Determine the tension developed in cables $OD$ and $OB$ and the strut $OC,$ required

to support the $50$ kg crate. The spring $OA$ has an unstretched length of $0\mathrm{.}8$ m and a

stiffness kOA $=1\mathrm{.}2k\frac{N}{m}.$ The force in the strut acts along the axis of the strut.