Question

Figures show the two different spinning poses of a ballet dancer.

1. In which spinning pose, the ballet dancer has more angular speed?

2. State the principle used by the ballet dancer to increase his angular speed.

3. “In the above situation, rotational kinetic energy is not conserved” – Justify this statement.

Answer 1

1. The pose shown in figure (B).

2. Statement of conservation of angular momentum.

3. I₁ω₁ = I₂ω₂

1/2 I₁²ω₁² = 1/2 I₂²ω₂²

I₁(1/2 I₁ω₁²) = (1/2 I₂ω₂²)I₂, I₁ > I₂

(1/2 I₂ω₂²) > 1/2I₁ω₁²