A person with outstretched arms, is spinning on a rotating stool. He suddenly brings his arms down to his sides. Which of the following is true about his kinetic energy K and angualr momentum L?

Options

A. K remains constant, L increases
B. K increases but L remains constant
C. Both K and L remain unchanged
D. Both K and L increase

Answer

B

Explanation

In the absence of any external toque, his angular momentum (L) remains constant. But `I_(1)omega_(1)=I_(2)omega_(2)`.
In this case, the particles of his body will come closer to the axis of rotation. Hence his moment of inertia will decrease and the angular velocity will increase and the K.E. will also increase.