A thin-walled cylinder with open ends is subjected to constant torque of 150,000 lb-in. The cylinder is made of 2024-T3 Aluminium with a yield strength Y=50 ksi. The cylinder has a mean radius r=5in and a wall thickness of 0.05inches. While holding the torque constant, an internal pressure ‘po’ is increased from zero until the cylinder begins to yield. What is the internal pressure at onset of yielding based on Tresca criteria?