Question

A ballet dancer is rotating about his own vertical axis at an angular velocity $100rev/min$ on smooth horizontal floor. The ballet dancer folds himself close to his axis of rotation by which his moment of inertia decreases to half of initial moment of inertia. His final angular velocity is :

• A. $50rpm$
• B. $100rpm$
• C. $150rpm$
• D. $200rpm$

Answer 1

The correct option is D $200rpm$

By using angular conservation, we have $I_1{N}_1=I_2{N}_2$,

Given $I_2=I_1/2$, ( putting the equation in the earliar equation)

$I_1\times 100=\frac{I_1{N}_2}{2}$

$N_2=200rpm$