Amechanism used in printing machinery consists of a tension assembled with a preload of 30 n. the wire diameter of spring is 2 mm with a spring index of 6. the spring has 18 active coils. the spring wire is hard drawn and oil tempered having following material properties: design shear stress 680 mpa modulus of rigidity 80 kn/mm2 determine: spring 1. the initial torsional shear stress in the wire; 2. spring rate; and 3. the force to cause the body of the spring to its yield strength.