A child stands at the centre of a turn table with his two arms outstretched. The turn table is set rotating with an angular speed of `40` rpm. How much is the angular speed of the child, if he folds his hands back reducing the moment of inertia to `(2//5)` time the initial value ? Assume that the turn table rotates without friction.
(b) Show that the child's new `K.E.` of rotation is more than the initial `K.E.` of rotation. How do you account for this increase in `K.E.` ?

Explanation

(a) 100 rev/min (use angular momentum conservation).
(b) The new kinetic energy is 2.5 times the initial kinetic energy of rotation. The child uses his internal energy to increase his rotational kinetic energy.