Question

if the external torque acting on a system is 0 then what will happen to its angular accleration and angular momentum

Answer 1

We know that torque, τ = I α where I is the moment of inertia and α angular acceleration.

If τ = 0, α = 0 since I ≠ 0.

And we know that τ = dL / dt where L is the angular momentum.

τ = 0 => dL / dt = 0

This implies that the angular momentum L remains constant.