A thin cylinder contains fluid at a pressure of 30 kg/cm$^2$. The inside diameter of the shell is 60 cm and the tensile stress in the material is to be limited to 900 kg/cm$^2$. The shell must have minimum wall thickness of
- A. 1 mm
- B. 2.7 mm
- C. 10 mm
- D. 9 mm
Answer: C. 10 mm
Explanation: Hoop stress $\sigma = Pd/2t$. $900 = (30 \times 60) / 2t \implies 1800t = 1800 \implies t = 1$ cm = 10 mm.