Correct answer: α = 10 rad/s²
The torque τ is given by τ = F × R. Using τ = I × α, where I for a solid cylinder is (1/2)mR², we solve for α: α = τ/I = (F × R) / ((1/2)mR²). Substituting F = 30 N, R = 0.4 m, and m = 3 kg, we get α = (30 × 0.4) / (0.5 × 3 × 0.4²) = 10 rad/s².