Which expression correctly gives the polar moment of inertia J for a hollow circular shaft (outer diameter D, inner diameter d)?

• A. J = π/32 * (D^4 - d^4)
• B. J = π/32 * (D^4 + d^4)
• C. J = π/32 * D^4
• D. J = π/32 * d^4

Answer: (A)