Problem 4 two wrenches apply torque to a steel pipe that can sustain a maximum shear stress of 125 mpa. the outer diameter of the pipe is 30 mm and the inner diameter is 20 mm. a)determine the stresses acting on two elements on the free surface of the pipe at a cross‐section through point a (i. e., think of this as a reference state of stress): a. one on the top that lies in the xz plane, b. the other on the side that lies in the xy plane. b)determine the factor of safety against failure in shear