Rotation 2 Question 7
7. A child is standing with folded hands at the centre of a platform rotating about its central axis. The kinetic energy of the system is $K$. The child now stretches his arms so that the moment of inertia of the system doubles. The kinetic energy of the system now is
(a) $2 K$
(b) $K / 2$
(c) $K / 4$
(d) $4 K$
(2004)
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Answer:
Correct Answer: 7. (b)
Solution:
- From conservation of angular momentum ( $I \omega=$ constant $)$, angular velocity will remain half. As, $K=\frac{1}{2} I \omega^{2}$
The rotational kinetic energy will become half.
