The angular momentum L for a point mass moving on a circle of radius r with speed v is:

• A. L = r m v
• B. L = m v / r
• C. L = m r^2 v
• D. L = F r

Answer: (A)

Angular momentum is defined as L = r × p, with p = m v. In circular motion, the radius vector r is perpendicular to the velocity v, so the angle between r and p is 90 degrees and sin(90°) = 1. This gives L = r p = r (m v) = m v r. So the magnitude of angular momentum is m v r, which is the form shown. The direction is along the axis perpendicular to the plane of motion, following the right-hand rule. The other forms don’t come from the cross product in circular motion: they would have incorrect dependence on r or incorrect units, so they don’t describe the angular momentum for this scenario.