Question

Two identical discs are placed one over the other and both are rotating about an axis through their common centre and normal to their plane at an angular velocity $\omega$. If the upper disc is suddenly removed, angular velocity of the other disc is :

• A. $\omega$
• B. $\frac{\omega }{2}$
• C. $2\omega$
• D. $4\omega$

Answer 1

The correct option is C $2\omega$

Let the initial MI be $I$ , then final MI will $I/2$

Using angular momentum $I_1{\omega }_1=I_2{\omega }_2$

We get $I\omega =\frac{I{\omega }_2}{2}\Rightarrow {\omega }_2=2\omega$