Question

Two particles, each of mass m and speed v, travel in opposite directions along parallel lines separated by a distance d. Show that the vector angular momentum of the two particle system is the same whatever be the point about which the angular momentum is taken.

Answer 1

Let at a certain instant two particles be at points P and Q, as shown in the following figure.

We infer from equation (iv) that the angular momentum of a system does not depend on the point about which it is taken.