In orthogonal turning of a cylindrical tube of wall thickness $5 \: mm$, the axial and the tangential cutting forces were measured as $1259 \: N$ and $1601 \:N$, respectively. The measured chip thickness after machining was found to be $0.3 \: mm$. The rake angle was $10^{\circ}$ and the axial feed was $100 \: mm/min$. The rotational speed of the spindle was $1000 \: rpm$. Assuming the material to be perfectly plastic and Merchant’s first solution, the shear strength of the material is closest to
- $722 \: MPa$
- $920 \: MPa$
- $200 \: MPa$
- $875 \: MPa$