Gere & Goodno — Torsion: Problem 3.3-7

3.3-7 While removing a wheel to change a tire, a driver applies forces $P = 100\text{ N}$ at the ends of two of the arms of a lug wrench (see figure). The wrench is made of steel with shear modulus of elasticity $G = 78\text{ GPa}$. Each arm of the wrench is $225\text{ mm}$ long and has a solid circular cross section of diameter $d = 12\text{ mm}$. (a) Determine the maximum shear stress in the arm that is turning the lug nut (arm $A$). (b) Determine the angle of twist (in degrees) of this same arm.