Lift a hemispherical dome filled with water by rotating it

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Discussion Overview

The discussion revolves around a physics problem involving a hemispherical dome filled with water that can be lifted by rotating it around its vertical line of symmetry. Participants explore the concept of angular velocity and its effects on the dome's ability to lift, questioning the mechanics involved in this scenario.

Discussion Character

  • Homework-related, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant claims to have calculated the minimum angular velocity required to lift the dome as 2.91 rad/s, while another states the correct answer is 1.95 rad/s.
  • Several participants express confusion regarding the concept of angular velocity and its role in lifting the hemisphere, questioning how rotation contributes to the lifting mechanism.
  • Another participant raises a concern about the conservation of momentum, suggesting that the idea of rotation causing translation may contradict established physical principles.
  • Clarification is sought regarding whether it is the water or the hemisphere that is being lifted, indicating uncertainty about the problem's specifics.

Areas of Agreement / Disagreement

Participants generally do not agree on the mechanics of the problem, with multiple competing views regarding the role of angular velocity and the implications for lifting the dome. The discussion remains unresolved.

Contextual Notes

There are limitations in understanding the problem's assumptions, particularly regarding the definitions of angular velocity and the forces at play in lifting the dome. The relationship between rotation and translation is also not clearly established.

Bohr1227
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Homework Statement


A hemispherical dome filled with water, radius 2 m and weight 30 tons, can be lifted by giving it a constant angular velocity around its vertical line of symmetry. The dome has a hole on the top. Decide the minimum angular velocity.

My answer is 2.91 rad/s .
The correct answer is 1.95 rad/s.

Homework Equations


Shown in the attached picture.

The Attempt at a Solution


Shown in the attached picture.
phys.png
 
Last edited:
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I don't understand this problem . Angular velocity of what ? How does whatever it is act on the hemisphere to lift it ??
 
Nidum said:
I don't understand this problem . Angular velocity of what ? How does whatever it is act on the hemisphere to lift it ??
I'm sorry, I have tried to make the problem clearer now :)
 
How does rotating something cause translation? Sounds like a breach of conservation of momentum?

Edit: So the water isn't lifted, just the hemisphere?
 

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