Question

A particle is rotating about a fixed axis. The angular momentum of the particle about any point on the fixed axis is the same. True or False?

(a) True

(b) False

The question was posed to me during an interview.

My question is based upon Angular Momentum in case of Rotations about a Fixed Axis topic in section System of Particles and Rotational Motion of Physics – Class 11

Answer 1

Correct answer is (b) False

Explanation: The angular momentum of a particle rotating about a fixed axis is given by L = r X p. At any time the vector p is fixed. But from different points on the axis, we will get different r vectors. So, the cross product of r & p will be different. Hence, the angular momentum vector is different about different points on the axis.