Question

A circular turntable circulates about its normal axis with uniform angular speed $\omega$. A circular thick layer of ice and of radius much smaller than the table top rotates along with the table. The new angular speed ${\omega }^{{}^{\prime }}$ of the table when ice starts melting is

• A. ${\omega }^{{}^{\prime }}>\omega$
• B. ${\omega }^{{}^{\prime }}<\omega$
• C. ${\omega }^{{}^{\prime }}=\omega$
• D. Any of (a), (b) or (c)

Answer 1

The correct option is B ${\omega }^{{}^{\prime }}<\omega$

As the ice melts we see that the water moves towards the rim thereby increasing the moment of inertia. Thus using the principle of conservation of angular momentum $(I_1{\omega }_1=I_2{\omega }_2)$ ${\omega }^{\prime }$ decreases.