Correct Answer - Option 1 : 77.80 N/mm

^{2}
__Concept:__

Stress: Internal resistance offered by the material to the deformation given by,

\(σ = \frac {F}{A}\)

Where, F = Force, A = Area

__Calculation:__

__Given:__

Di = 40 mm, Do = 50 mm, F = 55 kN

Area, A = \(=\frac{\pi}{4}(D_o^2-D_i^2)=\frac{\pi}{4}\times (50^2-40^2)=706.85~mm^2\)

Using \(σ = \frac {F}{A}\)

\(σ = \frac {F}{A}=\frac{55\times 10^3}{706.85}=77.80~\) N/mm2