Question

A boy standing on a rotating table, with heavy spheres in his hands, suddenly brings his hands close to his body. Then
O Angular momentum of the system remains same
O Angular velocity of system decreases
O Angular momentum of system increases
Both (2) and (3)​

Answer 1

Answer:

When the person withdraws his hands to his chest, his moment of inertia decreases. No external torque is acting on the system. So to conserve angular momentum, the angular velocity increases.

Answer 2

Angular Momentum remains same (Option 1)

The angular momentum of the system is given as follows:

$L = I \times \omega$

Now, torque in the system is given as :

$\tau = \dfrac{dL}{dt}$

When the boy on the rotating table with Spears on his hand takes the hand closer to the central axis (i.e. close to his body), the SYSTEM DOESN'T EXPERIENCE ANY EXTERNAL TORQUE.

So, $\tau$ is zero and 'dL' will be zero.

So, Angular momentum is constant .