A thin horizontal circular disc is rotating about a vertical axis pass...
As insect moves along a diameter, the effective mass and hence the M.I. first decreases then increases so from principle of conservation of angular momentum, angular speed, first increases then decreases.
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A thin horizontal circular disc is rotating about a vertical axis pass...
Explanation:
When the insect moves along a diameter of the disc, it is essentially moving from one side of the disc to the other. Let's analyze the scenario step by step to understand how the angular speed of the disc changes.
Initial Scenario:
- The insect is at rest near the rim of the disc.
- The disc is rotating about a vertical axis passing through its center.
- The angular speed of the disc is initially constant.
When the insect starts moving:
- When the insect starts moving along the diameter of the disc, it is essentially moving towards the center of the disc.
- As the insect moves towards the center, it covers a smaller distance in the same amount of time compared to when it was near the rim.
- This means that the linear speed of the insect decreases as it moves towards the center.
- According to the law of conservation of angular momentum, when the linear speed decreases, the angular speed must increase to maintain the same angular momentum.
- Therefore, as the insect moves towards the center, the angular speed of the disc increases.
When the insect reaches the center:
- When the insect reaches the center of the disc, it has covered the entire diameter and is now on the other side.
- At this point, the insect starts moving away from the center towards the rim of the disc.
- As the insect moves away from the center, it covers a larger distance in the same amount of time compared to when it was near the center.
- This means that the linear speed of the insect increases as it moves away from the center.
- According to the law of conservation of angular momentum, when the linear speed increases, the angular speed must decrease to maintain the same angular momentum.
- Therefore, as the insect moves away from the center, the angular speed of the disc decreases.
Conclusion:
- As the insect moves along a diameter of the disc, the angular speed of the disc first increases as the insect moves towards the center and then decreases as the insect moves away from the center.
- Therefore, the correct answer is option 'C' - the angular speed first increases and then decreases.
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