Five objects of mass m move at velocity at a distance r from an axis of rotation perpendicular to the page through point A, as shown below. The one that has zero angular momentum about that axis is:

Question

Five objects of mass m move at velocity  at a distance r from an axis of rotation perpendicular to the page through point A, as shown below. The one that has zero angular momentum about that axis is:

Quizplus · Accepted Answer

The angular momentum of an object rotating about an axis perpendicular to the page is given by L = Iω, where I is the moment of inertia and ω is the angular velocity.

The moment of inertia for five point masses of equal mass m at a distance r from an axis perpendicular to the page through their center of mass is I = 5mr^2/2.

Since all five objects have the same mass and velocity, they have the same angular velocity ω. Therefore, the object with zero angular momentum must have zero moment of inertia, which means it must be located at the axis of rotation.

Based on the diagram, the only object located at the axis of rotation is option D. Therefore, the answer is D.

Five Objects of Mass M Move at Velocity at a Distance