31. A mass M hangs on a massless rod of length l which rotates at a constant angular frequency. The mass M moves with steady speed in a circular path of constant radius. Assume that the system is in steady circular motion with constant angular velocity ω. The angular momentum of M about point A is 𝐿_𝐴 which lies in the positive z direction and the angular momentum of M about point B is 𝐿_𝐵. The correct statement for this system is : (a) 𝐿_𝐴 is constant, both in magnitude and direction (b) 𝐿_𝐵 is constant in direction with varying magnitude (c) 𝐿_𝐴 and 𝐿_𝐵 are both constant in magnitude and direction (d) 𝐿_𝐵 is constant, both in magnitude and direction

solution :     a 

A mass M hangs on a massless rod of length l which rotates at a constant angular frequency. The mass M moves with steady speed in a circular path of constant radius. Assume that the system is in steady circular motion with constant angular velocity ω. The angular momentum of M about point A is 𝐿_𝐴 which lies in the positive z direction and the angular momentum of M about point B is 𝐿_𝐵. The correct statement for this system is : (a)  𝐿_𝐴 is constant, both in magnitude and direction(b) 𝐿_𝐵  is constant in direction with varying magnitude(c) 𝐿_𝐴  and 𝐿_𝐵  are both constant in magnitude and direction(d) 𝐿_𝐵  is constant, both in magnitude and direction