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A light horizontal circular disc is spinning about a vertical axis through its centre. An insect initially remains at rest close to the edge of the disc. It then walks along a diameter to the opposite edge. While the insect is moving, the angular speed of the disc:

1. keeps decreasing throughout
2. keeps increasing throughout
3. increases at first and then decreases
4. stays the same

Correct answer: increases at first and then decreases

Solution

As the insect moves from the edge towards the center of the disc, it reduces the moment of inertia of the system, which causes the angular speed to increase due to conservation of angular momentum. However, as it reaches the opposite edge, the moment of inertia increases again, leading to a decrease in angular speed.

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