(i) Plane 20° clockwise to x-axis. Inclination with vertical (Fig. 2.15), \theta = 70° Normal stress,

\sigma_{\acute{x}} =\frac{o_x+o_y}{2}+\frac{o_x-o_y}{2} \cos 2 \theta-\tau_{x y} \sin 2 \theta =\frac{25}{2}+\frac{25}{2} \cos 140^{\circ}-(-100) \sin 140^{\circ}

= 67.2 MPa (Tension)

Shear stress,

\tau_{\acute{_x} \acute{_y}} =\frac{\sigma_x-\sigma_y}{2} \sin 2 \theta+\tau_{x y} \cos 2 \theta =\frac{25}{2} \sin 140^{\circ}-100 \cos 140^{\circ}

= 84.64 MPa (Clockwise)

(ii) Plane 20^{\circ} anticlockwise to x-axis.

Inclination with vertical (Fig. 2.15), \theta=110^{\circ}

Normal stress,

\sigma_{\acute{x}} =\frac{25}{2}+\frac{25}{2} \cos 220^{\circ}-(-100) \sin 220^{\circ}

= -61.35 MPa (Compression)

Shear Stress,

\tau_{\acute{_x} \acute{_y}} =\frac{25}{2} \sin 220^{\circ}-100 \cos 220^{\circ}

= 68.57 MPa (Clockwise)