An object is a solid disk with rotational inertia I = 0.09 kg·m^2 and angular velocity ω = 20 rad/s. What is its angular momentum?

An object is a solid disk with rotational inertia I = 0.09 kg·m^2 and angular velocity ω = 20 rad/s. What is its angular momentum?

• A. 1.2 kg·m^2/s
• B. 1.6 kg·m^2/s
• C. 1.8 kg·m^2/s
• D. 2.0 kg·m^2/s

Answer: (C)

Angular momentum for a rotating rigid body about a fixed axis is the product of its rotational inertia and its angular velocity, L = I ω. With I = 0.09 kg·m^2 and ω = 20 rad/s, compute L = 0.09 × 20 = 1.8 kg·m^2/s. The radian is dimensionless, so the units come out correctly as kg·m^2/s. This shows how L scales with both how much mass is distributed (I) and how fast the object spins (ω). The given numbers yield 1.8, the angular momentum.

Angular momentum for a rotating rigid body about a fixed axis is the product of its rotational inertia and its angular velocity, L = I ω. With I = 0.09 kg·m^2 and ω = 20 rad/s, compute L = 0.09 × 20 = 1.8 kg·m^2/s. The radian is dimensionless, so the units come out correctly as kg·m^2/s. This shows how L scales with both how much mass is distributed (I) and how fast the object spins (ω). The given numbers yield 1.8, the angular momentum.