The coiled spring is subjected to a force P. If We assume the shear stress caused by the s...

The coiled spring is subjected to a force P. If We assume the shear stress caused by the shear force at any vertical section of the coil wire to be uniform, show that the maximum shear stress in the coil is τmax = P/A + PRr/J where J is the polar moment of inertia of the coil wire and A is its cross-sectional area.