question_answer

When there is no external torque acting on a rotating body, which of the following quantities can change? (i) Angular acceleration (ii) Angular momentum (iii) Angular speed.

Answer:

                (i) The relation between torque and angular acceleration is \[\tau =I\alpha \]when \[\tau =0,\,\alpha =0\] \[\therefore \]Angular acceleration cannot change. (ii) The relation between torque and angular momentum is \[\tau =\frac{dL}{dt}\] When \[\tau =0,\,\,\frac{dL}{dt}=0\]or \[L=cons\tan t\] \[\therefore \]Angular momentum of the body does not change when torque is zero. (iii) As \[L=I\omega =cons\tan t\], when \[\tau =0\], therefore, angular speed \[(\omega )\]will change if moment of inertia (I) changes.