Topic: Machine Design
A 3 m long steel shaft has to transmit 7.5 kW at 3600 rpm. Required shaft diameter is given by (Take allowable shear stress = 100 N/mm², π² = 10)?
- A. 10 mm
- B. 7.5 mm
- C. 25 mm
- D. 12.5 mm
Answer: A. 10 mm
Explanation: Power P = 2πNT/60, so Torque T = (7500 * 60) / (2π * 3600) ≈ 375/(6π) N-m. From the torsion equation T/J = τ/r, and J = πd⁴/32, we get T = (τ * πd³)/16. Solving for d³, d³ = (16T)/(πτ) = (16 * 375*10³ / (6π)) / (π * 100). With π²=10, d³ ≈ 1000 mm³. So, d = 10 mm.