Question

An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his rotational kinetic energy about the axis of rotation?

Answer 1

Answer:

rotational kinetic energy increases

Explanation:

when an ice skater pulls his arms closer to his body there is no rotational torque because we know that torque = F×R here R is the distance and when arms are closer to body distance is very less so there will be no torque and so angular momentum is conserved but moment of inertia is also decreases and we know that rotational kinetic energy  =  $\frac{L^{2}}{2I}$  

where L= angular momentum

          I = moment of inertia

as moment of inertia decreases and angular momentum is conserved so using the formula rotational kinetic energy increases